The insurgency in Iraq will last at least a decade and American troops alone will not be able to defeat it, a senior US military officer in Baghdad has predicted.

Speaking on the eve of Iraq´s first free election for 51 years, the officer conceded: "Iraqis are the ones who will have to defeat the insurgency, not multi-national forces.

"It is not necessarily a growing insurgency but it is a resilient one," he told The Telegraph. "We´re looking at a long-term insurgency, probably at a lower level of violence than now. Historically, you look at a decade – and this is no different."

Iraq has been put under a virtual three-day lockdown for the elections, with unprecedented security measures bringing life to a standstill. There is a dusk-to-dawn curfew and travel between provinces is banned. Iraqi police officers will form an inner security ring at polling stations, bolstered by an outer ring of Iraqi troops, and American rapid reaction forces can be deployed if necessary.

"Undoubtedly, insurgents are going to attack polling sites with suicide belts wrapped around them,´´ Gen John Abizaid of US Central Command told an American newspaper. Another senior officer disclosed that 400 Iraqi civilians, officials and security officers had been killed so far this month as part of a campaign of intimidation against voters. He said that insurgents had stepped up their attacks on polling stations, with 45 targeted on Friday alone.

Yesterday, in what coalition commanders feared was a taste of violence to come, eight people died in a suicide bombing in the town of Khanaqin, north-east of Baghdad. In all, at least 18 people lost their lives at the hands of insurgents. Other attacks have been foiled, including one in Basra.

The Iraqi government also said that it had arrested three senior aides of Abu Musab al-Zarqawi, the alleged leader of al-Qa´eda in Iraq. Supporters of the terror mastermind, however, claimed that they had killed a candidate from the list of Ayad Allawi, the interim prime minister, and threatened to release a video recording of the death on the internet.

The US military official maintained that the insurgency was ultimately "doomed" to failure and said that a successful vote today could lead to a noticeable reduction in violence by April. The Iraqi forces were becoming more capable by the day, he said, and would eventually take responsibility for security: "From having the intelligence about who the insurgents are, to having the ability to identify and turn them in - all those things, Iraqis do best."

The cautiously optimistic assessment has led to the Pentagon drawing up "best case" plans to cut US troop numbers in Iraq by half over the next 18 months as part of a wide review of the American military, The Telegraph has learned.

It is hoped that a new strategy for training Iraqi troops – in which thousands of US military advisers would be attached to local units as "mentors" - will lead to dramatic improvements in security.

President George W Bush is insistent that America will not "cut and run", but the administration is keen to have an exit strategy ready before the US mid-term elections in late 2006 - as long as the "mentoring" strategy works.

"The administration does not want to go into the mid-term elections where they are now," said Dan Goure, a Pentagon adviser and director of the Lexington Institute defence think-tank. Generals and Pentagon civilian planners were working to cut numbers from about 120,000 - though there are 155,000 covering the elections - to 60,000.

Up to 10,000 American troops could be assigned long-term to Iraqi units, although US forces would still provide logistics back-up, air support and heavy armour. (© Copyright of Telegraph Group Limited 2004. 01/30/05)