Western leaders issued the threat of international intervention to set up “humanitarian corridors” in Syria on Thursday night after the UN warned that President Bashar al-Assad’s regime was failing to honour the terms of a ceasefire.

As foreign ministers gathered in Paris to discuss the crisis, Nicolas Sarkozy, the French president, compared the situation in Syria to that in Libya before the fall of Col Muammar Gaddafi and said the time had come to set up safe corridors for the provision of aid and to allow refugees to escape the fighting.

The Pentagon also warned for the first time that “all options” were on the table to resolve the conflict following a dire assessment from Ban Ki-moon, the United Nations secretary-general.

In a briefing to the Security Council ahead of last night’s Paris summit, Mr Ban said the situation on the ground in Syria was “highly precarious” and that attacks were on the rise, including the “shelling of civilian areas”.

He warned of “grave abuses by government forces” and demanded the regime immediately pull its heavy military equipment out of cities in accordance with Kofi Annan’s six-point peace plan.

Speaking as the meeting opened, Alain Juppé, the French foreign minister, said the failure of the Annan plan would lead to “civil war” . He said “several hundred” international monitors were needed in Syria to police the ceasefire.

The UN was on Thursday said to have agreed a preliminary deal with Damascus for the deployment of more peace monitors, however it was unclear what access or support they would be given. The UN is believed to want at least 300 on the ground.

Addressing the meeting of 14 states allied to the Syrian opposition last night, Mr Juppé said: “We cannot wait, time is short. The observers must be deployed fast and must be able to act without obstacles. The Annan plan is a guarantee of peace and freedom — its failure the path to civil, even regional, war.”

In a joint statement, the 14 nations said the Annan plan was the “last hope”. “Every day that passes means tens of new Syrian civilian deaths,” the statement said. “It is time to act.”

The meeting resolved that the “Friends of Syria” group, which includes France, the US, Saudi Arabia and Qatar, would do everything to ensure the UN plan succeeded. Earlier, Mr Sarkozy had compared Syria to Libya and repeated calls to create a safe passage for relief organisations to get food and medicine to about a million civilians.

“Bashar al-Assad is lying … He wants to wipe Homs off the map just like Gaddafi wanted to destroy Benghazi,” he said. “The solution is the establishment of humanitarian corridors so that an opposition can exist in Syria.”

Leon Panetta, the US defence secretary, said Mr Assad’s apparent success in beating off the insurgency with overwhelming military force meant he would “ultimately be brought down”.

“All options are on the table,” he said. “The department of defence is reviewing and continuing to review plans for a variety of possible scenarios should the president determine that further steps are necessary. We have looked at a variety of options including the possibility of developing humanitarian corridors.”

Hillary Clinton, the US secretary of state, on Thursday night said that Turkey was considering invoking Article 4 of the North Atlantic Treaty Organisation, which calls for consultation between all member countries if any of their “territorial integrity” or security is threatened. Last week, Turkey also threatened to invoke Article 5, which calls an attack on one Nato member — like Turkey — an attack on all members after Assad regime troops fired into its territory.

British officials said they were deeply opposed to humanitarian corridors, which would need to be patrolled by military forces and would represent a target for the regime. “The Syrian government is in theory willing to help facilitate unrestricted humanitarian aid, but when it comes down to it is preventing access,” one British official said.

On Thursday night, Syria’s rebel Free Syrian Army said it was time for outside military intervention even without Security Council approval.

The Pentagon was the most reluctant element in the US administration’s decision to go to war in Libya last year, and has not been keen in pushing military options in Syria. Mr Panetta last month said the administration was “focusing on diplomatic and political approaches”.

Thursday’s words, before the House Armed Forces Committee, are a considerable change of emphasis. In the past two weeks there have also been changes on the ground to lift humanitarian corridors or buffer zones, previously deemed too dangerous, up the agenda. (© Copyright of Telegraph Media Group Limited 2012. 04/20/12)