Iraqi insurgents on Friday overran a police station and detonated a car bomb near a Shia mosque in Baghdad, killing up to 30 people in the capital's worst day of violence since the US-led assault on Falluja.
The police station attack, the first of its kind in Baghdad, raised new questions over the viability of Iraq's parliamentary election, scheduled for January 30.
Police and national guard will be the first line of defence for polling stations, which insurgents have threatened to attack on election day.
"What they're trying to do is a hit-and-run operation," said Sabah Kadhim, a spokesman for the ministry of interior. "They go in with force trying to kill as many as they can."
In Friday morning's attack on the police station in the southern Baghdad neighbourhood of al-Amel, about 50 masked guerrillas drove up with machine guns and rocket-propelled grenades before storming inside, residents and police sources said.
The attackers then lined up at least 11 policemen on the roof and executed them, the residents said, in some cases cutting their captives' throats before releasing detainees held in the station and looting its arsenal.
Residents said that two Iraqi police cars which arrived during the fighting were quickly hit and set on fire. A US relief column arrived only after the station had been overrun.
In the second attack, a car bomb exploded during clashes between police and insurgents near a Shia mosque in the mostly Sunni neighbourhood of Adhamiya, killing at least 14 people.
An internet statement in the name of the al-Qaeda Iraq organisation of Jordanian militant Abu Musab al-Zarqawi took credit for the al-Amel assault, and for what it claimed was a raid on a police station in Adhamiya.
The statement praised "the destructive effect that such operations has on the morale of the enemy".
Attacks on police have been common elsewhere in Iraq.
On November 10 and 11 insurgents overran at least nine police stations in Mosul, Iraq's third-largest city, leading to the temporary disintegration of the police force there. But yesterday police in Mosul said their commandos repulsed an assault on a police station, killing 11 of the attackers.
Several hours after the assault on the Baghdad police station, smoke continued to pour from burning patrol cars outside. Spent cartridges and bullet marks peppering the station's concrete blast walls bore witness to the volume of the insurgents' fire.
Insurgents have used the neighbourhood surrounding the Baghdad police station, which contains housing developments populated by officials of the former regime, to stage attacks on the nearby airport road.
Both the US and UK embassies this week barred their staff from using the road after several attacks on vehicles.
Rebuilding an effective police force has been one of the biggest challenges facing postwar Iraq. Police ranked low on the social scale under the Saddamist regime, but have been thrust onto the front line of the insurgency.
Over the last three months, Iraq's interior ministry has established new special forces and other elite units, recruiting heavily from members of the old Iraqi army as well as from Kurdish former anti-Saddam guerrillas. The new units have won praise from coalition military officials, but faced intimidation, including threats of assassination or kidnapping against themselves or family members.
Additional reporting by Awadh al-Taee