A senior Iraqi customs official escaped a roadside bomb attack on Tuesday, officials said, the latest in a spate of assassination attempts ahead of provincial elections.

The blast struck the convoy carrying police Maj. Gen. Ahmed al-Attiyah, the director-general of Iraq's customs agency, as he was on his way to work in central Baghdad, officials said.

Al-Attiyah was not harmed, but three of his guards were wounded, according to police and hospital officials.

A car bomb also exploded near an Iraqi army patrol in the northern city of Mosul, killing one soldier and wounding two others, police said.

The officials spoke on condition of anonymity because they weren't authorized to talk to the media.

Nobody claimed responsibility for the attacks, but they occurred as tensions are high ahead of Saturday's provincial elections.

The vote is expected to redistribute power among Iraq's fractured ethnic and religious groups, and the U.S. military has warned it expects insurgents to try to disrupt it.

Meanwhile, a Sunni insurgent group claimed responsibility for downing two U.S. helicopters that crashed Monday, killing four U.S. troops, according to the SITE Intelligence Group, an organization that monitors extremist Web sites.

The claim could not be independently verified, but it appeared on Web sites commonly used by Islamic militants.

The U.S. military said the investigation was ongoing but Monday's crash in northern Iraq did not appear to be the result of enemy action.

In a Web posting, the Army of the Men of al-Nakshabandia Order said it used rockets to shoot down two U.S. Black Hawk helicopters and promised to release a video of the attack.

The group, which billed itself as a nationalist group, is part of an umbrella organization founded by ex-Saddam Hussein deputy Izzat Ibrahim al-Douri called the Supreme Council for Jihad and Liberation.

It said the attack occurred in the Hawija area in Tamim province, which includes the disputed oil-rich city of Kirkuk. The insurgents also claimed "more than 20 enemy members" died, although the U.S. military reported four dead in the crash, according to SITE.

The crash was the deadliest single loss of life for U.S. forces in Iraq in more than four months amid an overall decline in violence.