The Pentagon pulled all 12 B-1 bombers this weekend from the U.K.’s RAF Fairford air base to their home stations in the U.S. weeks after an alleged terror threat against a U.S.-operated post in England.

“While operational security precluded us from confirming the movement of our assets and forces in real-time, we can acknowledge now that all U.S. bombers that were deployed to RAF Fairford have re-deployed to their home stations in the United States,” a Pentagon official told The Hill on Sunday.

“The Airmen that operate America’s bomber force, including B-1s, B-2s, and B-52s, remain ready to deliver precision global strike capabilities – including through operations that launch and recover from the continental United States – anywhere, anytime,” the official added.

Flight trackers spotted multiple B-1 bombers departing the base, located in Gloucestershire, Sunday morning.

Officials did not reveal what prompted the rushed withdrawal of the heavy, long-range bombers that can carry a payload of both guided and unguided weapons.

The U.S. military has relied on the military base to base B-52 and B-1 bombers for the Trump administration’s war against Iran.

The withdrawal comes after British authorities arrested six men linked to a suspected attack on the air base that officials said was foiled. The U.K. police have released the suspects on bail, but the investigation into the incident has continued.

Five of the men involved in the incident were U.K. nationals in their 20s. Authorities have not released names of any of the men arrested in connection with the incident.

A U.K.-Iranian dual national who was arrested was released on bail, British authorities confirmed on Saturday.

British Prime Minister Andy Burnham said on Wednesday that the UK government believes that Iran “played a part” in the alleged thwarted attack on the base.

Iran has denied its involvement in a thwarted terrorist attack.