The US defence secretary has warned coalition troops in Iraq will not wait indefinitely for gunmen to surrender in the besieged city of Falluja.
America has not fielded conscripts since the Vietnam War
Donald Rumsfeld suggested the chance of a peaceful outcome was remote as militants resisting US marines are not involved in the negotiations.
The Dominican Republic has followed Spain and Honduras in announcing the withdrawal of its troops from Iraq.
A US senator has called for the draft to be reintroduced after three decades.
The US military reported killing eight militants in Falluja on Tuesday despite the truce there.
A spokesman said the men were seen brandishing rocket-propelled grenade launchers but described the flare-up as "minor".
The Americans have been demanding the surrender of the killers of four American security contractors in the city at the end of March as well as the handover of heavy weapons there.
Unofficial Iraqi sources estimate that up to 600 people have been killed during the siege of the Sunni Muslim city of 300,000 while the US military has lost scores of troops in the region.
Correspondents in Falluja say some families and local Iraqi police officers forced out by the fighting have now begun trickling back into the city.
Mr Rumsfeld said the current state of affairs in Falluja could not continue indefinitely.
"Thugs and assassins and former Saddam henchmen will not be allowed to carve out portions of that city and to oppose peace and freedom," he said at the Pentagon in Washington.
The defence secretary accused gunmen of "killing people and threatening the people of Falluja" and said negotiations had only involved "town fathers".
America's top soldier, Gen Richard Myers, said Falluja had to be "dealt with".
"We went in because we had to find the perpetrators and what we found was a huge rat's nest that is still festering today," the chairman of the Joint Chiefs of Staff said.
Earlier, a coalition spokesman, Gen Mark Kimmitt, told the BBC that offensive operations would resume unless heavy weapons were handed over but gave no timetable.
Gen Kimmitt also sought to play down reports of heavy civilian casualties in Falluja, saying the reports needed to be verified by the Iraqi government.
Coalition shrinks further
Senator Chuck Hagel, a senior Republican, has called for the return of military conscription, abolished in 1973 towards the end of the Vietnam War.
"There's not an American... that doesn't understand what we are engaged in
today and what the prospects are for the future," he said on CNN.
"Why shouldn't we ask all of our citizens to bear some responsibility and pay some price?"
The Dominican Republic has announced it will withdraw its 302 troops from Iraq within "the next week".
Dominican troops were attached to the 1,300-strong Spanish contingent.
Honduras announced it was withdrawing its 368 troops on Monday shortly after the new Spanish government said its troops would be gone within two months.
Spanish Foreign Minister Miguel Angel Moratinos has arrived in Washington for talks on Wednesday with State Secretary Colin Powell.
The BBC's Justin Webb reports from the city that their session is not likely to be a meeting of minds.