At least 20 people were killed and more than 50 wounded Saturday in a suicide car bombing outside the Iraqi National Guard headquarters in the northern city of Kirkuk.

In a separate incident, a car bomb hit a U.S. convoy in Baghdad, wounding three soldiers. American forces responding to that incident were caught in a second explosion that killed two soldiers and wounded eight others.

An Islamic Web site posted a statement purportedly from the Tawhid and Jihad group claiming responsibility for the Baghdad attacks, but the statement's authenticity could not be immediately verified.

Also Saturday, hospital workers in Fallujah said a U.S. airstrike in the city left four people dead and three others wounded. The U.S. military has carried out a number of previous airstrikes targeting militants in the city.