US warplanes and attack helicopters killed about 70 militants around the western Iraqi city of Ramadi, the military said on Monday, after a landmark referendum that appeared to have ratified a new constitution.
Local people said some of the dead were civilians although the US military said it had no such reports.
Election officials slowly counted up to 10 million ballots from Saturday's referendum, with partial results pointing to a clear win for a charter Washington hopes will help establish Iraq as a stable democracy able to do without US troops.
The violence in Ramadi, a rebellious city about 110 km (68 miles) west of Baghdad, highlighted the challenge posed by Sunni Arab insurgents opposed to the US-backed constitution.
Few people in Ramadi voted, yet for the first time, many Sunnis elsewhere in Iraq took part in the referendum, even if a large majority of them voted "No", provisional figures show.
Iraqis digested the news that the constitution had probably passed, with some hailing it as a good sign and others warning it could push the chaotic country closer to complete breakdown.
"If the constitution passes without consideration for the voters who said 'No', it will lead to a sectarian war," said Faisal Houmud, 37, a merchant in the Sunni bastion of Falluja. "This a dilemma for the Americans and the Iraqi government."
Sunni politicians were divided on the issue but several conceded that the constitution would come into force come what may. They would thus focus their energies on a December 15 election to boost their power to amend it in parliament.
"The nationalist forces are determined to participate in the next election," said Fakhri al-Qaisi of the National Dialogue group.
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A US military statement said the Ramadi battle occurred on Sunday and involved US jets, helicopters and ground troops.
It said at least 20 militants were killed when an F-15 aircraft bombed a group of men burying a roadside bomb - one of the deadliest weapons in the insurgent arsenal. Another 50 insurgents were killed in a series of separate strikes, the statement added, saying military commanders had no indications of any US or civilian casualties in the operation.