WASHINGTON (Reuters) – The Pentagon has ordered five military ships and thousands of Marines and sailors to help transport U.S. citizens out of Lebanon, a move that could sharply speed up the evacuation as fighting continues.

The U.S. Navy said on Tuesday the Iwo Jima Expeditionary Strike Group and the 24th Marine Expeditionary Unit were ordered to head to the area to help evacuate thousands of Americans.

The group includes the three ships in the Iwo Jima group — the helicopter carrier USS Iwo Jima, amphibious transport dock USS Nashville and the dock landing ship USS Whidbey Island, together carrying 2,200 Marines and sailors.

Two other ships were also ordered to join the Iwo Jima — the amphibious transport dock USS Trenton and a High Speed Vessel Swift, a catamaran with an aluminum hull.

Helicopters from the Marine expeditionary force have evacuated 68 Americans over the past two days. Those flights continued on Tuesday, the Navy said.

The State Department has said about 25,000 Americans are in Lebanon, but a smaller number — about 15,000 — have registered with the embassy as living or traveling in the country. A defense official said the Pentagon had planned for the evacuation of an even smaller number — 5,000 to 8,000.

A spokesman for U.S. Naval Forces Central Command said the Iwo Jima group’s participation would significantly increase the number of Americans who could be evacuated quickly from Lebanon. But he could not offer additional details, saying the specifics depended on how the group’s ships and helicopters were used.

"That’s a tricky number because it depends on how they do it and there’s tons of different ways to do this," said Cmdr. Jeff Breslau.

The five ships should be in place to assist the evacuation within two to three days, Breslau said.

The ships are headed toward Lebanon from just south of the Suez Canal