NATO ambassadors adopted without debate on Wednesday an "operation plan" for the Iraq mission which foresees the despatch of "200 to 300" military instructors to Iraq under heavy guard, officials said.

But behind the scenes, sources said that Germany in particular is holding out against letting its NATO staff officers take part in the mission, despite the hard-won political green light given to the proposal by the envoys.

A "heated exchange" occurred between the US and German representatives during the ambassadors' meeting, one source said.

"This is a serious issue and one the secretary general is looking into very closely," another official with the North Atlantic Treaty Organisation said on condition of anonymity.

The official refused to say which countries were refusing to release their officers attached to NATO, but Germany along with Belgium, France and Spain has refused to have any military involvement in the US-led coalition in Iraq.

In total, about a dozen of NATO's 26 member states do not want to take part in the training mission, the alliance's supreme military commander, US General James Jones, said recently.

France is not directly involved in the row because it is outside NATO's integrated military command.

But De Hoop Scheffer expects other countries such as Germany that are in the structure to release their NATO officers for Iraq training duty.

"For this caveat ... to spread would be corrosive for the solidarity of the alliance. It is something the secretary general will resist," the official said.

NATO leaders agreed at a June summit in Istanbul to help train Iraqi security forces, but their ambassadors battled for months to agree on the details.

NATO finally decided last month to send up to 400 instructors, aiming to get the bulk of them there in time for January elections.

During a visit to NATO headquarters earlier this month, Iraq's interim prime minister Iyad Allawi urged the military alliance to rush its training officers into the country, warning that any delay "could cost lives".

Under the newly agreed operation plan, the instructors would train about 1,000 Iraqi officers a year at a military academy near Baghdad. De Hoop Scheffer hopes to have the mission up and running by the end of the year.

The outgoing chairman of NATO's Military Committee, German General Harald Kujat, said the latest hitch to the Iraq operation was "extremely regrettable".

"This integrated command structure must function when we need it to function," he said.

"Now we need to implement this decision (the operation plan), and for that it is important that everybody contributes to that."

Kujat added that NATO cannot force a sovereign state into an operation against its will, "but in the past we have had operations without the participation of all members".