Iraqi officials say they have arrested three top aides to Abu Musab al-Zarqawi. The news comes as a second U.S. military helicopter crashes, this time near Baghdad.

In separate news briefings Friday, Iraqi officials said the three men include Zarqawi's military advisor, his Baghdad commander and another close aide.

Zarqawi's group, al-Qaida in Iraq, has denounced Iraq's national election and vowed to continue attacks.

Meanwhile, the U.S. military said they are investigating the crash of a Kiowa Army helicopter in southwest Baghdad. The helicopter usually carries a crew of two, but there has been no word on casualties.

The incident follows Wednesday's crash of a Marine transport helicopter that killed all 31 military personnel on board.

In Baghdad Friday, insurgents killed five American soldiers in three separate attacks. Four Iraqis were also killed in a car bomb attack in southern Baghdad.

In recent days, insurgents have distributed flyers urging Iraqis not to vote in Sunday's election and vowing attacks on polling centers.

Some information for this report provided by AP and Reuters.