The United States has called for a "greater commitment" from Iraq's government in the fight against the Islamic State (IS) group.
U.S. Defense Secretary Ash Carter told a congressional hearing that the U.S. military had hoped to train 24,000 Iraqi security forces by this fall but had only received enough recruits to train about 9,000 so far.
"We simply haven't received enough recruits," Carter said.
"While the United States is open to supporting Iraq more than we already are, we must see a greater commitment from all parts of the Iraqi government."
Last week, the White House announced the United States would send up to 450 troops to a new base in the western Iraqi province of Anbar, mainly to advise the Iraqis on planning and execution of a counteroffensive against the IS fighters.
General Martin Dempsey, the top U.S. military officer, said he would not recommend regularly deploying small numbers of U.S. ground troops on the front lines, simply to "stiffen the spines" of the Iraqis.
Dempsey said Washington was facing similar challenges in recruiting enough Syrian opposition forces for a program to train and equip them to battle IS militants.