In separate comments, Rice and ambassador Ryan Crocker said foreign service officers were obliged by their oath of office to work at any diplomatic mission worldwide, regardless of the risks or their personal feelings about the policies of any administration.

"We are one foreign service and people need to serve where they are needed, " Rice said aboard her plane as she flew to Turkey for a weekend conference of top officials from Iraq's neighbours. Crocker is also attending the conference.

Rice noted that more than 1,500 of the 11,500 foreign service officers had already done Iraq duty voluntarily and, while understanding the safety concerns of those who might be ordered to go, said they must uphold their commitments.

"I would hope others would think about their obligation not just to the country but to those who have already served, " said Rice, who sent a worldwide diplomatic cable seeking volunteers for the 48 vacancies the US must fill next year in Iraq.

"Our mission in Iraq is the most essential foreign policy and national security priority for our nation, " Rice wrote in the unclassified cable. "Our success in Iraq and beyond will have lasting consequences for our country and the world. . .

I believe strongly that it is our duty to do our part toward succeeding in the vital mission in Iraq given to us by the president."

Crocker was even blunter, saying diplomats had to prioritise the US interest over their own safety and that those who did not were "in the wrong line of business".

Joining the foreign service "does not mean you can choose the fight", he told reporters in Dubai. "It's not for us to decide if we like the policy or if the policy is rightly implemented. It's for us to go and serve."

Crocker, a 36-year veteran diplomat who has worked throughout the Middle East and was sceptical of the Iraq war, has been the US ambassador to Iraq since early this year. He has repeatedly asked for more experienced staff to work at the embassy and in reconstruction. His requests have been given top priority by Rice and state department chiefs who have offered generous incentives, including extra danger pay, leave time and preference on next assignments to attract diplomats to volunteer for Iraq duty.