Suicide bombers killed at least 17 people on the same day Iraqi officials gave final approval to a security deal allowing U.S. troops to remain in the country for another three years.

A White House spokeswoman, Dana Perino, welcomed Thursday's widely-expected ratification by Iraq's presidential council.   She said the security agreement will help solidify Iraq's democratic gains and affirm Iraq's sovereignty.

Iraqi lawmakers have extracted some concessions from Washington in the deal, including a promise not to use Iraq to launch attacks against neighboring countries.  Iraqi opposition lawmakers also managed to insert a pledge that the pact will go before the public in a referendum within six months.

Meanwhile, two suicide truck bombers struck the city of Fallujah in western Anbar province on Thursday, killing at least 15 people, including Iraqi police officers.  Separately U.S. officials said a suicide car bombing killed two U.S. soldiers in the northern city of Mosul.

The U.S. military considers Mosul one of the last strongholds of al-Qaida in Iraq fighters.

In northeastern Diyala province, at least three people were killed when a bomb exploded near a restaurant in the capital, Baquba.

Wednesday, a top U.S. commander in Iraq, Lieutenant General Lloyd Austin, said the number of deadly attacks in the country fell in November to the lowest level since the beginning of the U.S.-led war in 2003.

Also on Thursday, Iraqi security officials said a mass grave containing some 80 bodies was found close to Baquba, a former Sunni insurgent stronghold.

Some information for this report was provided by AFP, AP and Reuters.