A car bomb exploded near a Kurdish party's office Tuesday in the northern city of Mosul, killing at least three Iraqi soldiers only days before pivotal elections, officials said.

Nobody claimed responsibility for the attack, which occurred amid rising tension as the Kurds have been jockeying for power primarily with Sunni Arabs in Saturday's provincial elections.

The blast occurred near the offices of the Kurdish Democratic Party, or KDP, which is headed by Kurdish leader Massoud Barzani.

Iraqi security forces became suspicious of the vehicle, which blew up as a team approached to inspect it, an army officer said.

The officer, who spoke on condition of anonymity because he wasn't authorized to release the information, said two soldiers and a civilian also were wounded.

Hisham al-Gourani, a KDP official in Mosul, said the explosion took place about 100 yards (90 meters) from the KDP office but the Kurds suffered no casualties.

The nationwide balloting for provincial council members is particularly heated in Ninevah province, which includes Mosul, because of fierce ethnic and sectarian rivalries.

Sunni insurgents also remain active in the area despite numerous U.S.-Iraqi military operations.

Sunnis have a slight majority in the province, but they boycotted the January 2005 vote that filled the current 41-seat council, leaving the Kurds with a disproportionate share of power.

U.S. military commanders hope Saturday's elections will redistribute power on a fairer basis and bolster security gains by stanching support for the insurgency in Mosul and elsewhere.

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

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

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.

In an Internet statement that could not be independently verified, 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 U.S. military denied the claim, saying the two helicopters that went down were OH-58 Kiowa Warriors and "there were no reports of enemy action or contact prior to accident."

Maj. Derrick Cheng, a spokesman for U.S. forces in northern Iraq, said an investigation was under way to identify the cause.

The insurgent 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, according to SITE, although the U.S. military reported four dead in the crash.

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.