Insurgents have stormed two security targets in the town of Falluja, west of Baghdad, triggering a gun battle which killed at least 22 people.
At least 30 people were also wounded in the attack
The daylight raid by masked gunmen was the third major attack on Iraqi defence forces this week, following bombings that left around 100 people dead.
Many prisoners were freed from a police station as attackers went from room to room throwing hand grenades.
Fourteen police officers and three gunmen were reported among the dead.
The same security compound in the flashpoint town was attacked two days earlier during a visit by the top US commander in the Middle East, Gen John Abizaid. He escaped unharmed.
Up to 50 men took part in the latest raid, which also left about 30 people injured.
"Unknown men fired mortars, explosives and light machine guns from four directions," police officer Earazan Abu Issa told Reuters news agency.
"Their weapons were more powerful than
our Kalashnikovs," he said.
The gunmen reportedly shouted "God is great" and "There is no God but Allah".
None of the prisoners released were suspected of involvement in the anti-US insurgency, police said.
The gunmen also attacked the local mayor's office, about a kilometre away, police said.
The BBC's Barbara Plett in Falluja said there was a lot of hostility and anger in the town.
Hours after the attack armed men in plain clothes roamed the streets and kept watch outside the hospital, some reportedly relatives seeking revenge.
There was no sign of American forces in the town, which lies in an area known as the so-called Sunni Triangle - the heartland of the guerrilla campaign against the US-led occupation of Iraq.
The latest attack adds to fears that the Iraqi police cannot protect themselves, let alone anyone else, our correspondent says.
POLICE STATION ATTACKS
14 February 2004: At least 22 killed in gun battle outside Falluja station
10 February: At least 45 die in blast in Iskandariya
31 January: Nine killed in blast outside Mosul station
14 December 2003: Car bomb in Khalidiya kills 17
22 November: At least 18 die in twin bombings in Baquba and Khan Bani Saad
As the violence continues, diplomatic efforts are under way to establish a stable political order in the country.
But a UN envoy assessing the feasibility of holding early elections in Iraq ended his visit on Friday without holding out any prospect that they could take place soon.
Lakhdar Brahimi told a news conference in Baghdad that big questions had to be answered before anyone could even begin discussing election dates.
A spokesman for the Iraqi Governing Council told the BBC that Iraq's key concern was the entry of foreign fighters into the country from neighbouring states.
In Kuwait, the foreign ministers of Iraq and its neighbours are due to discuss security concerns on Saturday.
It is the first time that an Iraqi representative is attending such a meeting.
The BBC's Jonny Dymond in Baghdad reports that many of Iraq's neighbours are deeply unhappy about the continuing US-led occupation and some do not want to give legitimacy to the coalition-selected Governing Council.