BAGHDAD, Iraq - A car bomb exploded today at a Shiite mosque in the capital, killing eight people and wounding 20, police said.

Meanwhile, a militant group claimed responsibility for shooting down a Russian-made helicopter Thursday carrying 11 civilians, including six Americans.

The blast happened during midday prayers at Al-Subeih mosque, in the capital's eastern New Baghdad neighborhood, said police Col. Ahmed Aboud. Police sealed off the area around the mosque, which was heavily damaged by the explosion.

Shiite mosques and funerals have become a frequent target of Sunni-led insurgents. In February, suicide bombers attacked a number of them during the Shiite commemoration of Ashoura, killing nearly 100 people.

The violence was part of a surge of dramatic attacks that have caused heavy casualties in recent weeks, ending a relative lull since January elections.

In northern Iraq, a roadside bomb exploded near a U.S. Army patrol today, killing one soldier and wounding another, the military said. The early morning attack happened north of Tal Afar, a city about 90 miles east of the Syrian border, which has seen frequent clashes between U.S. and Iraqi forces.

At least six other people, including three foreign civilians, were killed in additional bombings and shootings in Ramadi and Baghdad on Thursday.

Thursday's chartered flight was believed to be the first civilian aircraft shot down in Iraq since the U.S.-led invasion two years ago. The dead included six American bodyguards for U.S. diplomats, three Bulgarian crew and two security guards from Fiji, officials said.

The helicopter went down about 12 miles north of Baghdad. Associated Press Television News footage showed burning wreckage from the craft and personal belongings scattered across a wide area.

U.S. officials could not confirm the cause of the crash. However, the Bulgarian Defense Ministry said the helicopter was struck by missile fire.

A group calling itself the Islamic Army in Iraq posted a video on the Internet Thursday purporting to show the shooting of a survivor.

The authenticity of the footage, posted on a Web forum often used by militant groups, could not be confirmed. A U.S. Embassy official in Baghdad said he had no knowledge that anyone on board survived the crash and was killed later.

"Heroes of the Islamic Army downed a transport aircraft belonging to the army of the infidels and killed its crew and those on board in the regions of al-Taji north of Baghdad," the group said in a written statement accompanying the video. "One of the crew members was captured and killed."

In the footage, which shows burning wreckage and two charred bodies, militants come across an injured man wearing a blue flightsuit lying in tall grass.

"It's broken," he says in accented English, apparently referring to his leg, as militants - unseen except in brief glances - tell him to stand up. "Weapons? Weapons?" the gunmen ask him in Arabic and English as he stands uneasily.

The gunmen tell him, "Go!", and the survivor starts to hobble away, holding his hands up toward them. The gunmen then open fire, shouting "Allahu akbar," or "God is great," with the bullets hitting his body. They fire more shots into his body on the ground.