US B-2 bombers struck and destroyed two ISIS camps in Libya overnight, with initial estimates that over 80 militants were killed, US officials told CNN Thursday.

The mission, which was confirmed in a later Pentagon statement and is expected to be the last, short-notice military operation ordered by President Barack Obama, was approved several days ago by the President, according to sources.
"They (the ISIS fighters) posed a security threat to Libya, the region, and US national interests," Pentagon spokesman Peter Cook said in a statement. "While we are still evaluating the results of the strikes, the initial assessment indicates they were successful."
A US defense official said the militants were seen immediately beforehand carrying weapons, wearing tactical vests, holding mortars and standing in formation. The number killed was not released by the Pentagon, but the initial estimate put the figure at over 80. There were no women or children in the area, the official said.
US surveillance aircraft had been watching the sites for weeks as fighters fled from Sirte on the coastline into what they perceived to be the safety of remote desert areas. But the isolation of the area gave those surveillance aircraft clear imagery showing military-aged males in several areas, according to officials.
The two camps that were destroyed were located about 28 miles southwest of Sirte, the Pentagon said.
In addition to the B-2 bombers, unmanned aircraft also took part in the strikes, the defense official said.
The strike did not happen initially because the rudimentary camps had moved and surveillance had to be conducted again.
The B-2s heavy bombers flying from the US were planning to bomb four camps, according to initial reports. Some of the sites may have been empty, with fighters having moved again. US Navy warships equipped with Tomahawk cruise missiles were also on standby but initial reports indicate they were not needed.
The President's approval of the strike underscores in the closing hours of his administration the difficulty of targeting ISIS fighters in dozens of countries around the world. Obama has increasingly relied on armed drones, bombers and special forces on the ground to go after these types of targets in Syria and Iraq.
"We are committed to maintaining pressure on ISIL and preventing them from establishing safe haven," Cook said, using another acronym for ISIS. "These strikes will degrade ISIL's ability to stage attacks against Libyan forces and civilians working to stabilize Sirte, and demonstrate our resolve in countering the threat posed by ISIL to Libya, the United States and our allies."