Car bomb explosion site near the Sayed Jabir mosque in Abu al-Khasib 20 kilometers south of Basra

The U.S. military in Iraq announced the arrests of six men suspected in the Thursday downing of a civilian helicopter. Meanwhile, a series of explosions and insurgent attacks across Iraq left more than 12 people dead Saturday and injured dozens more. As Iraqi militants stepped up their attacks against Iraqi and foreign targets, a U.S. Army report cleared four top officers of any wrongdoing in the Abu Ghraib prisoner abuse scandal.

A tip by an Iraqi civilian led to Saturday's arrest of the six men U.S. authorities believe were involved in the shooting down of a civilian helicopter earlier in the week. The men were taken into custody overnight during raids on two houses where bomb-making material was also confiscated.

TV image shows commercial helicopter crash site north of Baghdad

The helicopter crash killed six American employees of a civilian security company and two security guards from Fiji. Two members of the Bulgarian flight crew were killed instantly. A third member survived the crash, but was executed by insurgents who were videotaping the wreckage.

The arrests came on a day when insurgents carried out a series of attacks across the country, including a car bombing that targeted an Iraqi National Guard convoy on the outskirts of Baghdad. The explosion killed nine Iraqi soldiers and injured another 20.

Earlier in the day a car bomb targeting a U.S. patrol detonated on the road to Baghdad's airport. Officials said one Iraqi was killed and 10 others wounded, including three American soldiers.

In southern Iraq, a car bomb exploded outside of Basra. Iraqi police Lieutenant Alla Saber said the bomb appeared to target a Shi'ite mosque.

He says a white Chevy Caprice exploded near the Shi'ite mosque. Two people were inside the vehicle at the time of the explosion.

Despite the surge in violence that has caused heavy casualties in recent weeks, President Bush vowed to stay the course. In his weekly radio address, the president thanked the U.S. Congress for approving his additional funding request for U.S. troops serving in Iraq and Afghanistan.

Mr. Bush said U.S. troops are working with Iraqi security forces, as they assume greater responsibility for the stability of the country.

"Today, more than 150,000 Iraqi security forces have been trained and equipped, and for the first time, the Iraqi army, police, and security forces outnumber U.S. forces in Iraq," president Bush said. "Like free people everywhere, Iraqis want to be defended and led by their own countrymen. We will help them achieve this objective, and then our troops will come home with the honor they have earned."

Meanwhile, the U.S. Army has cleared four top officers, including Lieutenant General Ricardo Sanchez, the former top American commander in Iraq, of any wrongdoing in the Abu Ghraib prisoner abuse scandal.

An Iraqi detainee at Abu Ghraib prison (File photo)

Iraqi detainees at Abu Ghraib were physically abused and sexually humiliated by military police and intelligence soldiers in the fall of 2003. Photos of some of the abuse caused worldwide condemnation when they were leaked to the media in early 2004.

General Sanchez had been criticized by previous investigations for leadership failures that may have contributed to prisoner abuse. But the Army's inspector general said the evidence did not back up those allegations.

However, the report did fault another military official, Army Reserve Brigadier General Janis Karpinski. General Karpinski oversaw the military police in charge of Abu Ghraib and has since been relieved of her command. It is expected that she will be given a written reprimand that will likely end her military career.

The Army Inspector General's report is the 10th investigation into the prisoner abuse scandal so far.