A U.S. Army helicopter went down Thursday south of Baghdad, and all nine aboard survived, although four were wounded, the military said.

Gunmen opened fire on a Black Hawk helicopter at about 7:30 a.m. as it flew over Latifiyah, 20 miles south of Baghdad, the official said, speaking on condition of anonymity because he was not authorized to release the information.

He had no word on casualties. Black Hawks, which can carry 11 fully equipped troops, are commonly used by the military to transport people in Iraq to avoid the dangers of roadside bombs and ambushes on the ground.

In other violence Thursday, 10 policemen were killed in an ambush in northern Iraq and a bomb killed 1 at a Sunni Muslim TV station, officials said.

The ambush occurred about 1 a.m. local time at a checkpoint near the Badush prison, some 45 miles southwest of Mosul, according to the officials, who said 10 policemen were killed.

The Iraqi government said Wednesday that it was extending a security crackdown in Baghdad to Mosul, 225 miles northwest of Baghdad, where violence has been on the rise after militants fled the operation in the capital.

A car bomb struck a Sunni Muslim television station, said Mahmoud al-Obeidi of the Iraqi Islamic Party that owns Baghdad TV. The party later said the assistant station director was killed and 12 others wounded in the blast.

Nobody claimed responsibility for the attack, but members of the Sunni Iraqi Islamic Party have been targeted in the past by suspected insurgents because they have joined the U.S.-backed political process.

The attacks came a day after U.S. military spokesman Maj. Gen. William Caldwell expressed disappointment at the high level of violence in Iraq despite a drop in the overall death toll in Baghdad during a U.S.-Iraqi security sweep that has entered its eighth week. The Iraqi government said it was extending the operation to confront spreading violence elsewhere in the country.

The military also said on Thursday that six U.S. soldiers killed in separate attacks in Baghdad earlier this week.

Two Multinational Division — Baghdad soldiers died and three others were wounded Wednesday after a roadside bomb struck their combat security patrol in southern Baghdad, the military said.

Two other Multinational Division — Baghdad soldiers also died and another was wounded Wednesday in a roadside bomb north of the capital, the military said.

On Tuesday, a Multinational Division — Baghdad soldier was killed by small-arms fire while on patrol in eastern Baghdad, a predominantly Shiite part of the city, the military said separately. No other soldiers were wounded in that attack, according to the statement.

Another Multinational Division — Baghdad soldier on a foot patrol was killed by small-arms fire on the southern outskirts of Baghdad on Tuesday, the military said. Another soldier was wounded in that attack.

The helicopter went down in a rural area and U.S. forces had cordoned off the site, the official said. He had no information on casualties but said the militants apparently were using anti-aircraft heavy machine gun.

Latifiyah is part of the area dubbed the Triangle of Death because of frequent insurgent attacks.

The last helicopter incident in Iraq occurred on March 1, when an OH-58 Kiowa helicopter made a "hard landing" in northern Iraq leaving the two crew members wounded. A week earlier, ground fire forced the downing of a Black Hawk north of Baghdad.

A parked car exploded in front of Baghdad TV at about 1:30 p.m. in the western neighborhood of Jami'a, al-Obeidi said.

Shortly after the explosion, the station went off the air, although a photo of a mosque with readings from the Quran, the Muslim holy book, appeared after a while.

Al-Obeidi said the building damaged along with several cars in the area. Police said the car used in the attack was a small truck used to collect garbage and U.S. and Iraqi troops had cordoned the area. The U.S. military had no immediate comment.

AP Television News footage showed several cars and a truck on fire, thick black smoke rising over the station, and building debris strewn across the street in front of the station. Children gathered to watch rescue workers while a man carrying two plastic shopping bags of groceries strolled by, barely glancing at the violent aftermath in a capital city grown used to daily bomb blasts and mortar fire.