Defense Secretary Ash Carter said Wednesday that U.S. training of Iraqi and Syrian forces to fight the Islamic State has been slower than expected, raising doubts about a key part of the U.S. strategy to defeat the extremists.

Only about 7,000 Iraqi security troops have been trained so far, well below the Pentagon target of 24,000 by this fall, Carter told House lawmakers. In Syria, the Defense Department is still struggling to find candidates who could be trained as U.S. allies.

Carter’s comments were made amid growing skepticism in Congress about U.S. progress in the war against the Islamic State. The defense secretary blamed much of the delay in training Iraqi troops on Iraq’s Shiite-dominated government, many of whose members oppose efforts to bring Sunni Muslims into the fight. […]