Two U.S. defense officials say setting up a humanitarian safe zone for those caught in the crossfire in Syria can be done militarily but would require the Obama administration to shift troops around.

Democratic Sen. Dick Durbin said Wednesday that he and other senators want a safe zone to respond to massive humanitarian problems in Syria. He says they hope the United Nations or U.S. allies in the nation could help.

The chairman of the Joint Chiefs of Staff, Gen. Martin Dempsey, tells a Senate Appropriations panel that the U.S. military can establish a safe zone, but it would mean re-deploying forces stationed elsewhere.

Defense Secretary Ash Carter called it a "challenging" proposition and said it would be targeted by both Islamic State militants and Syrian government forces.