The United States, Britain and Iraq on Friday angrily dismissed a warning from U.N. Secretary General Kofi Annan that a military offensive in the Sunni stronghold of Fallujah could jeopardize the credibility of upcoming elections in Iraq.

In letters dated Oct. 31 and addressed to President Bush, British Prime Minister Tony Blair and interim Iraqi leader Ayad Allawi, Annan said using military force against insurgents in the city would further alienate Sunni Muslims already feeling left out of a political process orchestrated largely by Washington.

"I wish to share with you my increasing concern at the prospect of an escalation in violence, which I fear could be very disruptive for Iraq's political transition," Annan wrote to the three leaders.

"I also worry about the negative impact that major military assaults, in which the main burden seems bound to be borne by American forces, are likely to have on the prospects for encouraging a broader participation by Iraqis in the political process, including in the elections."

Annan's comments and criticism drew anger and frustration from U.S., British and Iraqi officials.

"I don't know what pressure he has to bear on the insurgents," Allawi said in an interview with the BBC. "If he can stop the insurgents from inflicting damage and killing the Iraqis, then he's welcome -- we will do whatever he wants."

Annan pushed for a diplomatic, rather than a military, solution in Fallujah. But Allawi said the "window is closing" for diplomacy, and within hours U.S. warplanes pounded the heavily populated city while Marines and Iraqi troops hovered on the outskirts.

Asked about Annan's concerns Friday, State Department spokesman Richard Boucher said, "Frankly, we differ."

Boucher added: "The Iraqi government has made very clear that they do have a strategy for resolving the problems of these towns like Fallujah. It's a strategy that has worked in some cases already, in Najaf and Samarra and a few other places. It's a strategy of reaching out politically to local leaders, of reasserting Iraqi government control and of moving militarily where that needs to be done, Iraqis and coalition forces together."

Secretary of State Colin L. Powell discussed the letter with Annan in a weekend phone call, and the U.N. chief met privately on Monday with John C. Danforth, U.S. ambassador to the United Nations. Privately, Bush administration officials said they were livid about the letter, which was sent two days before the U.S. presidential election.

U.N. officials said Annan was sensitive to the timing and concealed his written concerns from many of his staff members. The contents of the letters were made public Friday in an article in the Los Angeles Times.

The United Nations is helping Iraq prepare for elections, and U.N. officials said Friday in New York that 85 percent of the registration centers have been set up and that its eight election workers in Iraq will be joined by 17 more before the January vote.

The planned election has been a key goal of the Bush administration, which has insisted, despite continual violence and insecurity throughout the country, that voting will proceed as scheduled. Washington and London have pushed Annan to beef up the U.N. presence in the country, but humanitarian staff members in the organization have been reluctant to go to Iraq, mostly because of the violence but also because of resentment over a war that was conducted without U.N. approval.

Relations between Washington and the United Nations have been at an all-time low since the U.S. invasion of Iraq in March 2003. In August, the United Nations lost one of its top envoys and nearly two dozen staff members when insurgents bombed U.N. headquarters in Baghdad. Since then, U.N. staffers have fought attempts by Annan to send them back to the country while the insurgency continues.

But Allawi and his U.S. and British backers argue that the only way to restore security in time for the election is by fighting the insurgency.

The Iraqi leader, who spent years on the CIA payroll, is a member of the country's Shiite majority and faces strong opposition to the offensive from the country's Sunnis. The Association of Muslim Scholars, a group of Sunni clerics, threatened to sit out the election and mount a nationwide campaign against the vote.

Those threats, along with concern for civilian casualties, prompted Annan's letter.

"Ultimately, the problem of insecurity can only be addressed through dialogue and an inclusive political process," he wrote.