The US accuses Iraq of harboring al Qaeda members who have fled Afghanistan (via Iran.) Iran and Iraq condone (and to a certain extent, control) smuggling between the two countries. This includes moving people across the border. But Iraq also harbors secular/leftist Iranian rebels in Iraq. But this apparently does not prevent Iranian religious conservatives and Iraq from cooperating to assist al Qaeda members. The only openly active religious militants are operating in the northern Kurdish controlled territory, and these groups apparently receive support from Iran (even though the militants up there are Sunni.)