BAGHDAD, Iraq - U.S and Iraqi forces clashed with insurgents in northern Iraq on Saturday after launching an operation to destroy an alleged militant cell in the town of Tal Afar, the U.S. military said. At least eight people were killed and 50 wounded, hospital officials said.

A U.S. observation Kiowa helicopter made an emergency landing amid the clashes, though the crew escaped with minor injuries, the military said in a statement. It was not immediately clear why the helicopter was forced to land.

In Baghdad, meanwhile, several mortar rounds landed near a checkpoint in the Iraqi capital Saturday close to the heavily fortified Green Zone, which houses Iraqi government offices and the U.S. Embassy, a spokeswoman for coalition forces in Baghdad said.

It was not immediately known whether the shells caused any casualties.

Fawazi Mohammed, the head of the local hospital, said at least eight people died and another 50 were wounded during the clashes in Tal Afar. Many of the casualties were caused by a mortar shell explosion in a Tal Afar market, authorities said.

American soldiers killed two insurgents and captured another, while three Iraqi national guardsmen were hurt in the fighting, the military said.

A U.S. Stryker Brigade vehicle securing the helicopter's site later came under attack by rocket-propelled grenades, the military said. Troops fought back, killing two attackers.

In response to heavy enemy fire, soldiers on the ground were forced to call for air support and a warplane dropped a bomb near the town, the military said. It wasn't clear if there were any civilian casualties.

U.S. intelligence believes Tal Afar is being used as a haven by insurgents smuggling men and arms into Iraq from nearby Syria. It opted to launch the Saturday operation in a bid to flush them out, the military said.

In the Baghdad attack, the mortar rounds landed near the entrance to the Green Zone's convention center, where members of Iraq's 100-member transitional assembly, known as the Iraqi Council, gathered for a meeting.

Mortar rounds also exploded near the American-occupied Al-Rashid hotel, not far from the Green Zone, the spokeswoman said.

Also Saturday, saboteurs blew up an oil pipeline in southern Iraq, the latest attack targeting the country's crucial oil industry, police and oil officials said.

Firefighters struggled to put out the blaze caused by the explosion near Hartha, 19 miles north of Basra, and technicians were forced to shut down the pipeline, said police Maj. Col. Nouri Mohammed.