BAGHDAD — A bomb struck a municipal council building today in Baghdad's Shiite Sadr City district, killing four Americans, including two soldiers and two U.S. government civilian employees, U.S. officials said. At least six Iraqi civilians also died.

U.S. troops captured a suspect who tested positive for explosive residue after fleeing the scene, the military said. It blamed Shiite extremists for the attack.

The blast occurred at 9:30 a.m., about half an hour before a scheduled meeting to elect a chairman of the local council in the Shiite militia stronghold, an Iraqi official said, speaking on condition of anonymity for security reasons.

The bomb exploded in the office where the meeting was to have occurred, the official said, adding that at least three council members were seriously wounded.

The district council office is in a southern section of Sadr City that is largely controlled by U.S. and Iraqi troops following weeks of fighting in the area.

A U.S. military statement said one U.S. soldier was wounded in addition to the two soldier fatalities. U.S. Embassy spokeswoman Mirembe Nantongo said the American civilians included one State Department and one Defense Department employee.

U.S. Secretary of State Condoleezza Rice, in Berlin for a conference on Palestinian security, was informed of the attack shortly after it occurred and spoke with U.S. Ambassador to Iraq Ryan Crocker about the incident, according to State Department spokesman Sean McCormack.

U.S. troops sealed off the building and the area.

An official of the Iraqi Interior Ministry said six Iraqi civilians were killed and 10 others wounded. He spoke on condition of anonymity because he wasn't authorized to release the information.