The US government has enlisted Britain´s help in a bid to stop a ship suspected of carrying Russian attack helicopters and missiles to conflict-riven Syria, The Sunday Telegraph can reveal.

The MV Alaed, a Russian-operated cargo vessel, is currently thought to be sailing through the North Sea after allegedly picking up a consignment of munitions and MI25 helicopters - known as "flying tanks" - from the Russian Baltic port of Kaliningrad.

Washington, which last week condemned Moscow for continuing to arm the Syrian regime, has asked British officials to help stop the Alaed delivering its alleged cargo by using sanctions legislation to force its London-based insurer to withdraw its cover.

Under the terms of the current European Union arms embargo against Syria, imposed in May last year, there is a ban on the "transfer or export" of arms and any related "brokering" services such as insurance. Withdrawal of a ship´s insurance cover would make it difficult for it legally to dock elsewhere and could force it to return the cargo to port.

The request to London from US officials comes after the US Secretary of State, Hillary Clinton, disclosed on Tuesday that Moscow was in the process of shipping a batch of attack helicopters to Syria.

Dismissing Russian government claims that its weapons sales to Syria would not be used for internal repression, Mrs Clinton warned the shipment could "quite dramatically" escalate the conflict, which has already claimed an estimated 10,000 lives. Yesterday, the United Nations monitoring mission said it had suspended its work because of "intensifying" violence on either side, which was putting its teams of unarmed observers at risk.

The helicopters Mrs Clinton was referring to are believed to be part of a 36-strong consignment ordered by the Syrian government at the end of the Soviet era, some of which were transferred back to Russia recently for routine maintenance. They are understood to have been serviced by the state-owned helicopter manufacturer, Mil, at their premises at Factory 150 in Kaliningrad.

While the Kremlin, which has so far vetoed calls for a United Nations arms embargo against Syria, insists that Mil is merely honouring the terms of an existing business contract, critics point that such helicopters have helped spearhead President Bashar al-Assad´s attempts to suppress the uprising against him. Last week it was reported that helicopters had repeatedly fired rockets at a hospital in a rebel enclave outside Aleppo in northern Syria.

Shipping records show that on Thursday - the most recent date for which data is available - the Alaed was off the north-west coast of Denmark, apparently heading south towards the entrance to the English Channel. It is insured by Standard P and I Club, which is managed by Charles Taylor and Co Ltd of London, whose offshore syndicate director, Robert Dorey, confirmed on Saturday that they were investigating claims that the ship was carrying arms.

"We were informed on Friday evening that the ship might be carrying weapons, in particular attack helicopters, missiles and non-specific munitions, and we are making inquiries to establish what their side of the story is," said Mr Dorey. "There are exclusion clauses in our cover, and for anyone involved in improper or unlawful trade, we can cancel cover. We are investigating whether or not to do so in this case."

Like most international cargo ships, the Alaed has a complex ownership and management structure. Its registered owner is Volcano Shipping on the island of Curacao in the Dutch Antilles, but it is listed as part of a fleet belonging to a Russian company, FEMCO, which was unavailable for comment last night. According to FEMCO´s website, the ship´s commercial management and chartering is carried out by United Nordic Shipping, a Danish company based in Copenhagen, but yesterday, United Nordic shipping said that the management agreement had never actually been finalised, and that FEMCO´s website was wrong.

"To the best of our knowledge the vessel is managed and operated by FEMCO in Russia," said Soeren Andersen, United Nordic Shipping´s managing director. "We have no knowledge of or involvement in the vessel´s current charter or trading - a fact we have also satisfactorily accounted for to the Danish authorities."

A source close to United Nordic added: "The Danish authorities contacted us a few days ago to ask about the ship, and said it was related to possible shipments of weapons to Syria."

The claims about the Alaed´s cargo will fuel the growing row over Russian involvement in supplying arms to Syria, which Moscow has long seen as a strategic partner because of the Russian naval base in the Syrian port city of Tartus.

Last week, The Sunday Telegraph disclosed how the Professor Katsman, a ship belonging to a firm owned by a Russian billionaire, Vladimir Lisin, docked in Syria with a suspected weapons cache on May 26, one day after the massacre of more than 100 people in the Syrian village of Houla.

Dr Lisin, a steel magnate who is also vice-president of the Russian Olympic Committee, now faces calls from British MPs to have his invitation to London 2012 withdrawn. Sources close the Games organisers have said, however, that accredited Olympic representatives of foreign countries enjoy an effective "diplomatic immunity" that would be revoked only in the most serious of circumstances.

On Saturday, Dr Lisin said that the accusations against him were "groundless" and said an internal investigation he ordered at his transport firm, Universal Cargo Logistics (UCL) had found no evidence that the cargo was dangerous or violated international law. "The evidence I was presented with indicates that according to the documentation the company was not transporting arms for either side of the Syrian conflict," Dr Lisin said in emailed comments. "To date, I have not received a single [piece of] evidence to the contrary. If at some point someone does bring such evidence to my attention, I shall be grateful and will take all the possible measures available to me."

UCL said that as part of its investigation it requested information on the Professor Katsman´s cargo from the owner, which it named as another Russian company. The company told UCL that the containers the Professor Katsman delivered to Syria "was a general cargo of non- military purpose featuring electrical equipment and repair parts (rotor blades) in containers and wooden crates", he said.

Dr Lisin is reported to be one of Russia´s richest men and is well- connected to the country´s political elite. Victor Olersky, a former board member of Dr Lisin´s shipping firm, North Western Shipping Company, is now a Russian deputy transport minister, while Dr Lisin himself has been photographed meeting both the Russian president, Vladimir Putin, and the Russian prime minister, Dmitry Medvedev. Dr Lisin also described calls to bar him from the Olympic Games as opportunistic "self promotion."

"I am against armed conflict in any region of the world, including Syria," he said. "Sadly, there are those who try to use the tragedy of the Syrian people for self-promotion... At the same time, I would like to ask those who consider themselves to be reasonable and responsible to refrain from groundless accusations that will do nothing more than aggravate the relations between people, businesses, and states.

"I have no doubt that the International Olympic Committee, the National Olympic Committee of the United Kingdom, and the Organising Committee of the 2012 Olympics will preserve the traditions of the Olympic movement that has always been above political gambling." Meanwhile, Russia and the West are at further loggerheads over Moscow´s plans to press ahead with a deal to supply President Assad´s regime with state-of-the art attack jets.

In a move that US intelligence officials fear could plunge the Syrian conflict into even greater long-term bloodshed, the Kremlin is pushing on with an existing 2007 contract to provide two dozen Mig- 29M2 fighter aircraft, estimated to be worth £250 million to the Russian defence industry. While the aircraft may not be ready for delivery for many months, Washington fears if President Assad´s regime is still intact it could use them to devastating effect against the country´s rebel enclaves. They could also be used to hinder any Western plans for a no-fly zone, which some analysts believe may eventually prove the only way to provide Syria´s rebel movement with a safe haven.

"Delivery of the Migs will helps prop Assad up and give him some credibility, which is not the message the US wants to see," said Washington-based national security analyst John Pike. "The Migs would make it more difficult to enforce a no fly zone, and would increase the amount of time that the Syrian air force could survive, although possibly only by a matter of a few days."

Rafif Jouejati, spokeswoman for the Free Syria Foundation, a US-based Syrian activist group, said: "Russian arms are flooding into Syria. If Assad gets these new and advanced Migs it will be terrible – a fearful thing."

She dismissed Russian claims that the aircraft were largely to provide strategic air defences against Syria´s historic enemy, Israel. "It is preposterous to argue that Assad needs them as a defence against Israel with everything else that is happening right now."

She also claimed Mr Lisin ought to have ordered his shipping firms be more proactive in finding out what any ships heading to Syria contained.

"When your ship is taking a cargo to Syria – a country embroiled in civil war – it is your duty to know what that cargo contains. You can´t hide behind a lack of knowledge when little children are being slaughtered."

The Kremlin has dismissed Western criticisms of its arms policy to Syria as hypocritical, saying that other governments are also fuelling the conflict by arming anti-Assad guerrillas. The Daily Telegraph disclosed yesterday that representatives of the main rebel group, the Free Syrian Army, had held meetings with US government officials to discuss getting them to authorise shipments of heavy weapons, including missiles. British MPs are calling for Rosoboronexport, the Kremlin-owned arms export firm that has a monopoly on Russian arms exports, to be banned from exhibiting at the trade section of next month´s Farnborough Airshow. Last week, Rosoboronexport had a stall at the Eurosatory 2012 arms exhibition in Paris, where videos of Russian attack helicopters were on display. Igor Sevastyanov, the company´s deputy CEO, said: "No-one can ever accuse Russia of violating the rules of armaments trade set by the international community. "The contract (with Syria) was signed long ago and we supply armaments that are self-defence rather than attack weapons."

On Monday Caroline Lucas, the Green Party MP for Brighton, raised the issue of Rosoboronexport´s attendance at Farnborough with the Foreign Secretary, William Hague, in Parliament. She said: "It is deeply alarming that while the Russian state-owned company Rosoboronexport continues to sell weapons to the Syrian government – despite appalling state-sponsored atrocities in the country – it will nevertheless be allowed to exhibit its wares on UK soil at Farnborough International Airshow.

"The Foreign Secretary has assured me in Parliament that he will look into the matter, but with the air show only a few weeks away, I would urge him to act now to prevent Rosoboronexport from entering altogether."

She added: "By taking measures to ban Rosoboronexport from Farnborough and revoke Mr Lisin´s invitation to the Olympics, the United Kingdom can lead by example in showing that it is prepared to take a moral stand against all of those foreign companies accused of involvement in the sale of weapons to deadly and undemocratic regimes."

An FCO spokesman said that Mr Hague was still considering the matter, but added: "Farnborough International Air Show is a commercial event run by Farnborough International Ltd. The British Government plays no part in deciding which companies are invited to the event." Asked about the Alaed last night, a spokesman for the Foreign Office said it was “urgently looking into any possible breaches of the EU arms embargo on Syria.”

“We are aware of reports that a ship carrying a consignment of refurbished Russian-made attack helicopters is heading to Syria and that it is travelling in international waters near the UK,” the spokesman added. “The Foreign Secretary made clear to Russian Foreign Minister Lavrov when they met on 14 June that all defence shipments to Syria must stop. We are working closely with international partners to ensure that we are doing all we can to stop the Syrian regime’s ability to slaughter civilians being reinforced through assistance from other countries.”

Additional reporting by Bill Lowther in Washington, Peter Allen in Paris, and Justin Stares in Brussels (© Copyright of Telegraph Media Group Limited 2012. 06/17/12)