The Pentagon says members of the Free Syrian Army who went through the new U.S. training program to fight Islamic State militants have been captured by the al-Qaida-linked Nusra Front in Syria.

Navy Capt. Jeff Davis says the military is monitoring the situation but details are sketchy.

Two U.S. officials said they believe that about five of the Syrian forces were taken sometime over the weekend, but it wasn't clear where they were captured or exactly how many may be missing.

The officials spoke on condition of anonymity because they weren't authorized to discuss the details publicly.

The kidnappings come on the heels of reports late last week that several moderate Syrian rebels going through the vetting process for the U.S. training program were captured by the Nusra Front.