The Pentagon is now training its third class of Syrian rebels in its plan to build a force to take on the Islamic State in Iraq and Syria (ISIS), a spokesman said Friday.

In total, the Pentagon is now currently training two classes, in a sign that the program is speeding up after a shaky beginning.

"We currently have two classes in training, and we continue to see significant interests and opposition forces volunteering for the program," U.S. Central Command spoesman Col. Pat Ryder said Friday.

ADVERTISEMENT

Members of the first class of 54 rebels deployed into Syria last month, only to be attacked by forces the Pentagon believes are al Nusra militants.

One rebel was killed and five captured, according to defense officials. Some have reportedly vanished, prompting officials to acknowledge that the program has faced challenges.

"Certainly this past week highlighted some of the challenges associated with fielding the New Syrian Forces, but it's important to keep in mind the success doesn't hinge on one fight, or one event, and we're still in the early phases of implementing this program," Ryder said.

"We're continually applying lessons learned and working as a coalition to make the [train and equip] progam better," he added.

The program has produced only 54 graduates so far since it officially started training them in May.

The second class of rebels did not begin training until late July. The third class began sometime since July 24.

Ryder would not say when exactly the third class began training, out of concern for the recruits' safety.

The Pentagon has kept details on the program as closely-held as possible, so as to protect them from ISIS and other groups when they redeploy back into Syria.

The recruits are training in Jordan, Turkey, Saudi Arabia and Qatar and have faced security challenges coming in and out of Syria for the training.

Despite the program's shaky start, the Pentagon hopes to ramp up the total trainees to 3,000 by the end of the year and 5,000 by next May.

The Pentagon plans to train and equip a force of 15,000 rebels by the end of three years, who can defeat ISIS and provide security in places where ISIS has been cleared.

The program has come under heavy criticism for moving too slowly and fielding too few rebels.

Congress approved the program in September and provided $500 million in funding in December, but defense officials say it took time to establish training sites and develop the training curriculum.

The Pentagon has also been carefully vetting the rebels.

Besides meeting basic requirements such as age and fitness, recruits must also not have links to extremist groups, pledge to target ISIS and not Syrian President Bashar Assad, and agree not to engage in any human rights abuses or atrocities.

Some also left the program for Ramadan, a Muslim holiday, and did not return.

But officials say thousands have volunteered and hundreds are in the pipeline, being vetted for training.