BAGHDAD, Iraq - The government today announced the arrests of two close associates of Abu Musab al-Zarqawi, including the chief of the terror mastermind's Baghdad operation. The announcement came two days before historic elections that extremists have vowed to subvert.

Insurgents, meanwhile, targeted more polling sites across the country, and a suicide car bomber killed four policemen in the capital. U.S. fighter jets thundered through the skies over Baghdad throughout the morning in a show of force against the militants.

U.S. troops and insurgents exchanged fire on a major Baghdad thoroughfare. The crackle of gunfire could be heard over the noon call to prayer.

Qassim Dawoud, a top security adviser, told reporters that the arrests of the al-Zarqawi lieutenants occurred in mid-January but gave few details. Dawoud said one of the men, Salah Suleiman al-Loheibi, headed al-Zarqawi's Baghdad operation and had met with the Jordanian-born terror leader more than 40 times over three months.

The other was identified as Ali Hamad Yassin al-Issawi.

On Thursday, al-Zarqawi's al-Qaida affiliate in Iraq posted a video on the Internet showing the murder of a candidate from Prime Minister Ayad Allawi's party.

Today's suicide car bombing rattled Baghdad's Doura neighborhood, a flashpoint in recent days, with several street battles between insurgents and Iraqi National Guard troops, and with assassinations of government officials.

Also today, insurgents shelled a U.S. Marine base south of Baghdad, injuring three American troops and three civilians, the military said.