The U.S. has moved surveillance drones into the skies over Libya to gather intelligence and get a better picture of what's going on in case additional military strikes against Islamic State militants are authorized.

The top U.S. military officer told a Senate committee that the Pentagon has shifted assets to Libya, based on recommendations from the U.S. commander for Africa.

The chairman of the Joint Chiefs of Staff, Gen. Joseph Dunford, told the Senate Armed Services Committee that the decision was made more than a month ago to increase resources for U.S. Africa Command.

U.S. officials say the decision allows the Pentagon to shift unmanned aircraft to Libya. Dunford says he agrees with assessments that there are about 6,000 Islamic State militants in Libya.