Karbala, Iraq ? In the biggest rebel attack since Saddam Hussein’s capture, suicide bombers and assailants with mortars and grenade launchers blasted coalition military bases and the governor’s office in this southern city Saturday, killing 13 people and wounding at least 172.

The death toll in Karbala included six coalition soldiers — four Bulgarians and two Thais; six Iraqi police officers; and a civilian.

At least 172 people, many of them civilians caught in the chaos, were wounded in three nearly simultaneous assaults apparently designed to test the resolve of Washington’s allies in the coalition governing Iraq. A Polish-led force is responsible for security around the holy Shiite city of Karbala.

Also Saturday, Iraq’s U.S.-led administration put bounties of $1 million each on the heads of 12 remaining fugitives from the coalition’s list of the 55 most-wanted Iraqis.

Administrators already are offering $10 million for information leading to the capture or death of the 13th remaining fugitive — Izzat Ibrahim al-Douri, a senior official in the former regime and a Saddam Hussein confidant who now is the most wanted man in Iraq.

Insurgents also may have targeted this city 70 miles south of Baghdad on the assumption that military targets there would be more vulnerable to attack. The most intense rebel activity is in Sunni areas west and north of Baghdad, where combat-tested American troops have more experience fending off suicide bombers and other assailants.

One of four suicide bombers in Karbala gained entry to a Bulgarian camp, cutting through roadblocks in a car and destroying a building where the headquarters of the unit was located, Bulgarian Deputy Defense Minister Ilko Dimitrov said in Sofia.

Four Bulgarian soldiers were killed and 27 others were wounded, Dimitrov said.

A car bomb also killed two Thai soldiers on guard duty when the vehicle rammed into the walls of their camp.

A university building watchman receives help after he was injured in one of several bomb attacks in Karbala, Iraq. At least 13 people died Saturday during attacks on military bases and the governor's office.

President Bush called the prime ministers of Bulgaria and Thailand to express his condolences Saturday.