A parked car bomb struck northern Baghdad on Wednesday, killing at least four civilians and wounding six, police said. The explosion occurred about 11 a.m. in the district of Qahira, police Lt. Ali Mitaab even as Iraqi authorities deployed tens of thousands of troops in a major crackdown on security in the violence-prone capital. Mitaab said four civilians were killed and six were wounded. On his way back to Washington from his Iraq visit President George W. Bush said earlier Wednesday he will not bend to political pressure for troop withdrawals from Iraq and says he told worried leaders in Baghdad the United States will not leave until Iraqi forces can do the job. "I assured them they didn't need to worry," Bush said Tuesday. "I am going to do what I think is right. When I tell you these decisions are going to be made by General (George) Casey, I mean it," the president said. Casey is the top US general in Iraq. "There's a worry almost to a person that we will leave before they are capable of defending themselves, and I assured them they didn't need to worry," Bush said. "I also made it clear that we want to work with their government on a way forward on all fronts."