Baghdad ? A security pact with a timetable for pulling U.S. forces from Iraq won final government approval Thursday, even as suicide bombers killed 17 people and wounded more than 100. Two Americans were among the dead.

The brazen attacks — the deadliest in the heavily guarded city of Fallujah — raised questions about Iraq’s ability to ensure its own security as the U.S. scales down its combat role under the newly ratified U.S.-Iraqi pact, which calls for an American pullout within three years.

Iraq’s three-member presidential council signed off on the pact, removing the last legal barrier so that the agreement can take effect Jan. 1. It also requires American soldiers to leave the cities by the end of June.

Approval by the presidential council came one week after parliament approved the agreement, which was hammered out during months of tough negotiations that at times seemed on the point of collapse.

President Bush called Prime Minister Nouri al-Maliki and President Jalal Talabani to thank them for their work on the pact, the White House said.

The latest bombings came in cities where the U.S. military has struggled for years to maintain order and underscored the fragility of Iraq’s security gains. They added new urgency to U.S. efforts to train and equip an Iraqi security force capable of maintaining order after American troops have gone home.

The two Americans were killed when a suicide driver detonated an explosive-laden car near an Iraqi checkpoint in the northern city of Mosul, military spokesman Lt. Col. Dave Doherty said. Iraqi police said eight people were wounded, most of them civilians.

In Fallujah, once the symbol of Sunni Arab resistance to the U.S. occupation, truck bombers struck within minutes of each other outside the concrete barriers surrounding two police stations in different parts of the city, killing 15 people, wounding more than 100 and shattering nearby buildings, police and hospital officials said.

An al-Qaida front group, the Islamic State of Iraq, purportedly claimed responsibility for the attack in a statement posted on a militant Web site.

The thunderous blasts could be heard across the city of about 400,000 and sent giant plumes of black smoke rising over the dust-brown buildings.

“I was drinking tea in my house when a big explosion took place. It was like an earthquake,” said Saad Ibrahim, a 34-year-old mechanic who lives near one of the police stations. “I could hear the cry of a child trapped in a house. … We tried to help him, but the police and firefighters arrived and asked us to leave the area.”

Local authorities announced a curfew and closed all exits and entrances to the city. Police said the blasts were so huge that investigators could not find the chassis or the engines of the two trucks used in the attacks.

“It looks like the trucks evaporated,” a senior police official told The Associated Press.

All the police and hospital officials spoke on condition of anonymity because they weren’t authorized to release the information.

U.S. commanders say that attacks are down 80 percent nationwide since last March but that al-Qaida and other militants remain capable of staging limited but high-profile attacks.