Four B-52 bombers are being deployed to the Middle East in response to what administration officials said earlier this week are threats of a possible attack by Iran or allied fighters on American troops in the region. Two of the bombers are expected to leave Tuesday from Barksdale Air Force Base in Louisiana, arriving at Al Udeid Air Base in Qatar on Wednesday, CBS News national security correspondent David Martin reports.

White House national security adviser John Bolton said on Sunday that the U.S. was deploying a bomber task force and the USS Abraham Lincoln Carrier Strike Group to the U.S. Central Command region, an area that includes the Middle East. Bolton said the movement was in response to "a number of troubling and escalatory indications and warnings." He didn't provide details, but said the U.S. wants to send a "clear and unmistakable" message to Iran that "unrelenting force" would meet any attack on U.S. interests or those of its allies.

"The United States is not seeking war with the Iranian regime, but we are fully prepared to respond to any attack, whether by proxy, the Islamic Revolutionary Guard Corps, or regular Iranian forces," he said.

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A Defense Department official told CBS News' Martin earlier this week the U.S. has detected "a number of preparations for possible attack" on U.S. forces at sea and on land.

"There is more than one avenue of attack or possible attack that we're tracking," the official said.

The official said the decision to order the deployment was made on Sunday.

The USS Abraham Lincoln has filed with Egypt for permission to go through the Suez Canal and is expected to transit in the next 48-72 hours, Martin reports. The aircraft carrier was scheduled to go to the Gulf anyway but is now going one to two weeks early.

CENTCOM is expected to request additional forces, including Patriot anti-missile batteries.