The top U.S. military officer says the U.S. won't take shortcuts in screening Syrian rebel volunteers for a U.S. training program, which is off to an extremely slow start.

Upward of 6,000 Syrians have volunteered, but fewer than 100 passed muster.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told a Pentagon news conference Wednesday that while the U.S. needs to develop a credible, moderate fighting partner on the ground to battle the Islamic State in Syria, the vetting must be done carefully to weed out extremists.

Dempsey suggested that more credible volunteers may come forward after the Muslim holy month of Ramadan is over in mid-July. The training is being done in Jordan and Turkey.

The U.S. goal is to train and equip 5,400 rebels per year.