Mr Cocker warned in a cable obtained by the Washington Post that unless Iraqi employees were given hope of finding safe haven in America they would quit, weakening the ability of the Bush administration to make an impact in Iraq.

He said that Iraqis in US government employment "work under extremely difficult conditions, and are targets for violence including murder and kidnapping. Unless they know that there is some hope of a [visa] in future, many will continue to seek asylum, leaving our mission lacking in one of our most valuable assets".

The US government and its main coalition partner in Iraq, Britain, have both been criticised by human rights and refugee organisations for failing to allow significant numbers of Iraqi asylum seekers into their countries. The US has admitted 825 Iraqis since the invasion in 2003.

The British government granted asylum to about 100 Iraqis between 2003 and 2005, but figures since then are unknown. It has refused to consider applications from among the 2 million Iraqis who have fled to Jordan, Syria and other neighbouring states.

In the wake of heavy criticism, the Bush administration expanded its Iraqi refugee programme, promising to admit 7,000 by October. However, it has processed just 133 since last October.

The United Nations estimates that up to 20,000 Iraqis will never be able to return to Iraq. Other countries have accepted many more Iraqi refugees. Sweden has taken in more than any other nation, despite the fact that it is not part of the coalition.

Last week it emerged that Denmark had secretly airlifted out about 200 Iraqi interpreters and their families. The move was made in advance of the imminent withdrawal of 470 Danish troops stationed in Iraq.