BAGHDAD - Fourteen U.S. soldiers were killed Wednesday when a Black Hawk helicopter crashed during a nighttime mission in northern Iraq, but the military said it appeared the aircraft was lost by mechanical problems and not from hostile fire.
It was the Pentagon's worst single-day death toll in Iraq since January and indicated how forces are relying heavily on air power in offensives across northern regions after rooting out many militant strongholds in Baghdad and central regions.
But extremists are striking back.
A suicide truck bombing against a police station in the northern oil hub of Beiji claimed at least 45 lives -- 25 policemen and 20 civilians -- amid a series of deadly attacks north of the capital.
The growing bloodshed in the north carries a mixed message. It suggests some success for the U.S.-led security sweeps seeking to reclaim control of areas in and around Baghdad. But it also highlights the apparent resilience of groups such as al-Qaida in Iraq as they retaliate and seek new footholds.
The White House, meanwhile, sought to quiet a political tempest with Iraq's prime minister, Nouri al-Maliki.
President Bush, speaking to a veterans' convention in Kansas City, Mo., called al-Maliki "a good man with a difficult job." Bush added: "I support him."
Just hours earlier, al-Maliki lashed out at American criticism over his government's inability to bridge political divisions or stop the violence, warning he could "find friends elsewhere."
The spat appeared to ease, but al-Maliki's sharp words signaled a fraying relationship with his key backer nearly three weeks before Congress receives a pivotal progress report on Iraq.
The UH-60 helicopter went down before dawn in the Tamim province that surrounds Kirkuk, an oil-rich city 180 miles north of Baghdad, said Lt. Col. Michael Donnelly, a military spokesman in northern Iraq.
He declined to be more specific about the location of the crash, but said the facts gathered indicated it was almost certainly due to a mechanical problem and not hostile fire. The final cause remained under investigation, however.
The Black Hawk was one of two helicopters and had just picked up troops after a mission when it crashed, Donnelly said. The four crew members and 10 passengers aboard were assigned to Task Force Lightning, but the military did not release further information about their identities pending notification of relatives.
In Washington, a defense official said the helicopter was from the 25th Infantry Division's combat aviation brigade, based in Schofield Barracks, Hawaii.
A U.S. soldier also was killed and three others were wounded Wednesday during fighting west of Baghdad, the military said separately.
The total of 15 was the largest single-day death count since 25 U.S. soldiers were killed around the country on Jan. 20, including 12 who died in a helicopter crash. The deadliest crash occurred Jan. 26, 2005 when a CH-53 Sea Stallion transport helicopter went down in a sandstorm in western Iraq, killing 31 U.S. troops.
The U.S. military relies heavily on helicopters to avoid the threat of ambushes and roadside bombs -- the deadliest weapon in the militants' arsenal -- and dozens have crashed in accidents or been shot down.
Wednesday's deaths raised to at least 3,722 members of the U.S. military who have died since the Iraq war started in March 2003, according to an Associated Press count.
The Sept. 15 deadline for the Iraq progress to Congress leaves Bush little time to show that the U.S. troop buildup is succeeding in providing the enhanced security the Iraqi leaders need to forge a unified way forward.
U.S. commanders have warned that extremists would step up the violence this month in a bid to upstage the report, which comes amid a fierce debate over whether Bush should start withdrawing American troops.
A string of attacks hit across northern Iraq.
The deadliest strike blasted a police station in a residential area in Beiji, 155 miles north of Baghdad, according to police and hospital officials.
The officials, who spoke on condition of anonymity because they weren't authorized to release the information, said 25 policemen and 20 civilians were killed. The officials also said 57 civilians and 23 officers were wounded.
Jassim Saleh, 41, who lives about 500 yards from the blast site, said he saw an explosives-laden truck carrying stones ram the police station. But other reports described it as a fuel tanker.
"It was a horrible scene. I can't describe it," he said. "The bodies were scattered everywhere. I was injured in my hand and a leg, but I took three wounded people to the hospital in my car."
Brig. Gen. Kevin Bergner, a U.S. military spokesman in Baghdad, said the attack bore all the hallmarks of al Qaeda in Iraq, which appears to be trying to retrench in parts of northern Iraq.
"It appears to be something that is consistent with an al Qaeda-related attack," he told AP Radio in an interview.
Later Wednesday, a suicide bomber on a motorcycle set off a blast near four police vehicles parked near grocery stores in Muqdadiyah, about 60 miles north of Baghdad, killing six people, including two policemen, and wounding 35 people, police said.
A roadside bomb also targeted a police patrol in Tikrit, Saddam Hussein's hometown 80 miles north of Baghdad, killing one officer and wounding three people, authorities said.
Iraqi police and tribal officials also reported that a suicide truck bomber struck a joint U.S.-Iraqi outpost near Taji, a town near an air base 12 miles north of Baghdad. They said the attack occurred a day after tribal leaders who have turned against al Qaeda held a recruiting meeting, but no information about casualties was immediately available.
The U.S. military said only that a coalition outpost in the village of Hor al-Bashah had been attacked.
Suicide vehicle bombers have killed more than 2,315 Iraqis this year, according to an AP count. The tally far outpaces the January-August period last year when 441 Iraqi deaths were blamed on suicide bombers aboard vehicles.
