BAGHDAD -- US soldiers battled insurgents northeast of Baghdad yesterday in clashes that killed more than 50 people. Some guerrillas were said to be ''fighting to the death" inside Fallujah, where American forces struggled to clear pockets of resistance.
At least five suicide car bombers targeted US troops elsewhere in volatile Sunni Muslim areas north and west of the capital, wounding at least nine Americans. Three of the bombings occurred nearly simultaneously in locations between Fallujah and the insurgent stronghold of Ramadi, the US command said.
The zone between Fallujah and Ramadi was one of at least three areas yesterday in which insurgents pulled off almost-simultaneous attacks against US or Iraqi forces, suggesting a level of military sophistication and planning not seen in the early months of the insurgency last year.
Pressing their offensive in central and northern Iraq, insurgents attacked police stations, Iraqi security forces, US military convoys and oil installations across a wide area of the Sunni heartland.
In a speech found yesterday on the Internet, a speaker said to be Abu Musab al-Zarqawi, a Jordanian-born terrorist leader said to be operating in Iraq, called on his followers to ''shower" the Americans ''with rockets and mortars" because US forces were spread too thin as they seek to ''finish off Islam in Fallujah."
The worst reported fighting took place yesterday about 35 miles northeast of Baghdad after assaults, at almost the same time, on police stations in Baqubah and its twin city, Buhriz.
Gunmen abducted police Colonel Qassim Mohammed, took him to the Buhriz police station, and threatened to kill him if police did not surrender the station. When police refused, the gunmen tied the colonel's hands behind his back and shot him dead.
US and Iraqi troops rushed to the scene, setting off a gun battle that killed 26 insurgents and five other Iraqi police, Iraqi officials said.
At the same time, insurgents attacked a police station in Baqubah and seized another building. US aircraft dropped two 500-pound bombs before the end of the fighting, in which four American soldiers were wounded, the US command said.
During the fighting, US troops came under fire from a mosque, the US military said. Iraqi security stormed the mosque and found rocket-propelled grenades, mortar rounds, and other weapons and ammunition, the statement said.
In one of the car bombings along the Fallujah-Ramadi corridor, the attacker rammed into a Marine armored vehicle, wounding the four troops inside. The two other bomb attacks caused no injuries, including one in which the driver rammed his car into a tank but his explosives failed to explode.
Witnesses reported a fourth car bombing late yesterday in Ramadi against a US convoy, but no casualties were reported.
In Mosul, where an uprising broke out last week in support of the Fallujah defenders, a suicide driver tried to ram his bomb-laden vehicle into a US convoy, the military said. He missed his target but set off the explosives, wounding five soldiers, four of them slightly.
Four US soldiers were wounded when their patrol ran over a land mine yesterday near Beiji in northern Iraq, the military said.
Saboteurs blew up an oil pipeline yesterday, shutting down Iraqi oil exports from the north, and set fire to a storage and pumping station in northern Iraq, officials said.
In Baghdad after nightfall yesterday, heavy explosions rocked the Green Zone, the barricaded neighborhood that houses the Iraqi government and the US Embassy. Loudspeakers warned, ''Take cover, take cover."
Gunmen carried out near-simultaneous attacks on a police station and an Iraqi National Guard headquarters in Suwayrah, 25 miles south of Baghdad, killing seven Iraqi police and soldiers.
During a news conference in Baghdad, Interior Minister Falah Hassan al-Naqib, a Sunni Muslim, condemned the growing attacks on Iraqi police and security forces, calling them part of a campaign ''to divide this country and thrust it into a civil war."
''They are trying by all means to divide this country and to create an ethnic and sectarian war," Naqib said of the insurgents.
Prime Minister Iyad Allawi said police had arrested the leader of a militant group responsible for the killings of some foreign hostages. Moayad Ahmed Yasseen, leader of the group Muhammad's Army, was captured along with some of his followers, Allawi said. He did not say what kidnappings the group has been involved in.
But a statement by the prime minister's office later described Muhammad's Army as the ''armed wing of an organization created by Saddam Hussein" to fight for the return of the Ba'ath Party to power.
The spike in violence accompanied the US-led assault against Fallujah, the main insurgent stronghold, 40 miles west of Baghdad. The week-old offensive in Fallujah has left at least 38 US troops and six Iraqi soldiers dead.
The number of US troops wounded is 320, although 134 have returned to duty. US officials estimated more than 1,200 insurgents have been killed.
In a telephone interview with reporters at the Pentagon, Marine Colonel Michael Regner, operations officer for the First Marine Expeditionary Force, said US and Iraqi forces had captured more than 1,052 prisoners in Fallujah. Most are Iraqis, but some are foreigners.
''Very few of them are giving up," Regner said. ''They're fighting to the death."
He said US troops and Marines were working their way back from the southern part of the city toward the northern part, clearing out pockets of resistance and recovering caches of weapons.