BAGHDAD (AP) — Iraq’s presidential council on Thursday approved a security pact that sets out a three-year timeframe for U.S. troops to leave, a spokesman said, the final step for the agreement to replace a U.N. mandate that expires Dec. 31.

As the final legal hurdle to the deal was cleared, American soldiers and Iraqi civlians alike faced another round of deadly bombings by insurgents trying to chip away at recent security gains.

Two suicide bombers in explosives-laden trucks took aim at police stations in the former Sunni insurgent stronghold of Fallujah on Thursday, killing at least 15 people and wounding more than 100, Iraqi officials said.

A suicide car bomber also killed two U.S. soldiers and wounded nine Iraqi civilians near a checkpoint in the northern city of Mosul, the U.S. military said.

Iraq’s parliament signed off on the deal last week following months of tough talks between U.S. and Iraqi negotiators that at times seemed on the point of collapse. The entire process has been fraught with hardscrabble dealmaking between ethnic and sectarian groups.

In Washington, the White House welcomed Thursday’s decision.

White House press secretary Dana Perino said the Iraqi presidential council’s approval Thursday sets a path for American troops to come home and called the agreement a “remarkable achievement for both of our countries.”

Under the deal, which goes into effect Jan. 1, U.S. forces will withdraw from Iraqi cities by June 30 and the entire country by Jan. 1, 2012. But the agreement includes the caveat that it should go before voters in a referendum by the end of July — when the deal will already be in effect.

That was a concession to Sunni demands and means the agreement could be rejected next year if, for example, anti-U.S. anger builds and demands for an immediate withdrawal grow. By that time, however, American troops will likely have left urban areas and will be a less intrusive presence.

President Jalal Talabani, a Kurd, and his two deputies Tariq al-Hashemi, a Sunni Arab, and Adel Abdul-Mahdi, a Shiite, signed the accord at their headquarters in Baghdad, council spokesman Nasser al-Ani told The Associated Press.

Iraq also will gain strict oversight over the nearly 150,000 American troops now on the ground, representing a step toward full sovereignty for Iraq and a shift from the sense of frustration and humiliation that many Iraqis feel at the presence of American troops on their soil for so many years.

Followers of anti-U.S. cleric Muqtada al-Sadr opposed the measure, demanding an immediate withdrawal, and the Shiite leader has called for peaceful protests against the continued presence of American forces in Iraq.

The U.S. military has warned that the security gains of the past year remain fragile.