US forces have carried out an air strike on a suspected militant hideout in the Iraqi city of Falluja, the US military has said.
Falluja has been at the forefront of the insurgency
At least 20 people were killed in the raid, coalition officials said.
It is the third such strike this week on Falluja, where the US believes a key al-Qaeda leader is hiding.
Earlier, the interim Iraqi Prime Minister, Iyad Allawi, vowed to crush insurgents after one of the most violent days for months.
More than 100 people died in a wave of attacks on Iraqi cities on Thursday.
In continuing outbreaks of violence, three policemen died in an attack on a police station in Baquba on Friday, and a policeman was killed by a roadside bomb in Baghdad.
Hours before the latest air strike, US troops killed at least two militants in clashes in Falluja.
A US military statement said the latest air raid targeted "a known Zarqawi network safe house" in south-eastern Falluja.
"Wherever and whenever we find elements of the Zarqawi network, we will attack them," the statement said.
The US accuses Abu Musab al-Zarqawi of leading al-Qaeda militants inside Iraq and has offered a $10m reward for his capture.
Two US air strikes this week on suspected militant hideouts linked to Zarqawi in Falluja killed at least 40 people; residents and Iraqi security sources said civilians were among the dead.
Zarqawi's followers claimed responsibility for Thursday's attacks in a statement on an Islamic website.
But, masked fighters from Falluja appeared on a videotape denying Zarqawi was in the city, Reuters news agency reported.
"We know that this talk about Zarqawi and the fighters is a game the American invader forces are playing to strike Islam and Muslims in the city of mosques, steadfast Falluja," a militant on the tape was quoted as saying.
Braced for escalation
Mr Allawi said the attacks were meant to sabotage the transfer of power from the US-led coalition to an interim Iraqi government on 30 June.
"These are isolated incidents. We are going to defeat them... We have been expecting this escalation and we are expecting more escalation in the days ahead."
MONTH OF VIOLENCE
25 June: At least 20 die in US air strike on Falluja
24 June: At least 100 die in rebel attacks in five Iraqi cities
22 June: US says it kills 20 militants in Falluja air strike
21 June: Four US soldiers die in Ramadi ambush
19 June: At least 20 die in US raid targeting militants in Falluja
17 June: 41 die in car bomb attacks in Baghdad
16 June: Iraqi oil fields security chief killed in Kirkuk
14 June: 12 die in Baghdad car bomb
13 June: Education ministry official killed in Baghdad
12 June: Interim deputy foreign minister Bassam Qubba killed in Baghdad
8 June: Car bombs kill 15 in Mosul and Baquba
By the handover of formal sovereignty, the UN-approved interim government under Prime Minister Allawi and President Ghazi Yawer will have already been in place for a month.
The BBC's David Bamford says in that time Mr Allawi has not been shy in setting out where he thinks the process should go, and has signalled some key changes of direction from the policies of US administrator Paul Bremer.
Some ministries, he adds, have been up and running under Iraqi control for months and the coalition played up each handover as a transfer of sovereignty.
In a BBC interview, Mr Powell said those behind Thursday's attacks were trying to torpedo the handover.
"I think we underestimated the nature of the insurgency that we might face during this period," he said.
"The insurgency that we're looking at now has become a serious problem for us, but it's a problem that we will deal with."
But he said he hoped violence would tail off after the handover, once Iraqis saw that they had their own people in charge.