BAGHDAD, Iraq - A US Army helicopter made a "hard landing" in northern Iraq on Thursday, but the military said the problem was mechanical and not the result of hostile fire.

Iraqis watch as a US army 2nd Infantry Division soldier patrols central Baghdad, Iraq, Thursday, March 1, 2007. [AP]

Last week, ground fire forced a Black Hawk helicopter to make an emergency landing north of Baghdad, the military said. At least eight other US helicopters have crashed or been brought down by hostile fire in Iraq this year.

On Thursday, two pilots were injured and evacuated to an American military hospital in Kirkuk, about 180 miles north of Baghdad, the military said in a statement. There was no word on the extent of the pilots' injuries.

The helicopter, an OH-58 Kiowa, is mostly used in surveillance and some light combat missions.

"Preliminary reporting shows the cause of the hard landing was mechanical and not hostile fire," the statement said.

The military also announced the killing Wednesday of a US Marine in the western Anbar province, a hotbed of the Sunni insurgency. The Marine's name was withheld pending family notification.

The death brought to 79 the total number of Americans killed in Iraq in February. At least 3,163 members of the US military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count. The figure includes seven military civilians. At least 2,546 died as a result of hostile action, according to the military's numbers.

Baghdad appeared quieter Thursday, with only one person killed in a roadside bomb, police said. The lull came a day after a car bomb ripped through a bustling shopping district in western Baghdad, killing at least 10 people and wounding about 20.

Wednesday's blast in Baiyaa, a Sunni-Shiite neighborhood, sent flames and debris shooting two stories high, witnesses said. The force of the explosion peeled back corrugated tin roofs. Charred clothing still clung to the remnants of vendors' stalls hours later.

A US military spokesman condemned the bombing as "ruthless" and "barbaric" but said overall violence was down, three weeks into a joint US-Iraqi security crackdown.

"Although we've seen some initial progress, we know our enemies will continue to attempt to disrupt our efforts, and that improving security in Iraq will take time," Rear Adm. Mark Fox told reporters Wednesday.

On Thursday, the US military said American and Iraqi troops killed 10 militants and seized six weapons stashes in Diyala province northeast of Baghdad. The raids took place over the past three days, it said.

Diyala is a mixed Sunni-Shiite area that has seen increased violence in recent months, as insurgents stream out of Baghdad during a security crackdown there. Attacks on US troops are up 70 percent since last summer, and the number of arms caches discovered in Diyala has more than doubled in that time, US officials have said.

The 10 were killed Monday in Muqdadiyah, a town in Diyala about 60 miles northeast of Baghdad, the military said in a statement. Five others were detained in the operation.

Soldiers also discovered more than 50 rocket-propelled grenades, bomb-making materials and a stolen fire truck that was being loaded with explosives, the statement said.

Another cache was discovered the same day in Baqouba, the provincial capital of Diyala, that included a complete mortar system and 150 rounds of ammunition, the military said.

On Tuesday, a car bomb, TNT explosives and other bomb-making materials were confiscated in Baqouba as well, it said.