The US has withdrawn all of its bombers from RAF Fairford, the UK military base at the centre of an incident being investigated by counter-terror police.

A statement from a Pentagon official confirmed on Sunday it had removed its bombers- thought to be about a dozen B-1s - from the base back to their home stations in America.

The US did not give a reason for the withdrawal, but it follows a major incident on 27 September when police were alerted to three "suspicious vehicles" near the airbase.

Five men were initially arrested on suspicion of terror offences near the base and subsequently released on bail. A sixth man, a UK-Iranian national, was also later arrested and released on bail.

Whitehall sources have not disputed the decision from Washington was in response to the incident at the airbase in Gloucestershire.

The BBC has also been told it was a military rather than a political decision - taken at an operational level - and communicated from the US military to its British counterparts.

The UK's Ministry of Defence has not commented.

Tracking websites showed B-1 bombers flying out of RAF Fairford on Sunday.

The New York Times reported US commanders had received new threats about an Iran-backed plot against RAF Fairford according to two US officials.

The newspaper wrote the new information was part of the same threat warnings from three weeks ago, but officials acted quickly after specific details emerged in the past 24 hours.

The planes reportedly took off while aerial refueling aircraft were still being scrambled to support their flights to the US.

Days after the incident at RAF Fairford, Prime Minister Andy Burnham said there were "strong indications" that Iran had played a part in the incident but did not provide further details. Tehran has strongly denied any involvement.

Initially, five men aged between 23 and 25 were arrested in the early hours of the morning after vehicles were reported to be travelling towards the base operated by the US Air Force (USAF). All five were UK nationals from London.

They were arrested on suspicion of explosives offences and later on suspicion of preparing a terrorist act, before being released on bail in what police called an "investigative decision" that was "grounded in experience and strategy".

The sixth man, aged 25, was arrested in London on Thursday on suspicion of preparation of terrorist acts. Counter terror police confirmed on Saturday he had also been released on bail.

RAF Fairford has been used as a forward operating location by the USAF for decades.

In recent months, the US has flown B-1 and B-52 bombers from the base for the Middle East, after the UK approved a US request to use it for defensive strikes on Iran.

The withdrawal of the bombers comes as the US tries to recover from the damage inflicted on its aircraft by Iranian precision strikes.

It is technically possible for the US to conduct precision strikes directly from the US without a UK base - like in Operation Midnight Hammer last year.

But the removal of the bombers from RAF Fairford will remove a foothold for the country outside of continental Europe.

In July, Iran said "any base used for aggression against Iranian territory constitutes a legitimate target for our forces".

Days after the incident, and before the arrest of the sixth man, US Secretary of State Marco Rubio said on Fox News that it "clearly involve[d] the hands of a foreign actor".

Rubio did not provide further details - saying at the time he was limited on what he could say on air.

US President Donald Trump separately said he was "surprised" the five men had been released on bail.

"We know everything about them, we would not have released them," he said, adding that the UK had worked with the US "very closely" on this.

Many B-1 bombers flown from the UK were armed with precision-guided "bunker busting" bombs, with thicker casings to penetrate hardened or buried targets such as weapons stores.

They also carried air-to-surface missiles used against more heavily defended targets deeper inside Iran.

Each bombing mission, depending on the location of the target, would likely have taken around 12 to 15 hours in total there and back, with air-to-air refuelling both ways.

The Pentagon has stressed its bombing aircraft remain able to conduct missions "anywhere, anytime", including through "operations that launch and recover from the continental United States".

RAF Fairford base was occupied by USAF Strategic Air Command during the Cold War and later the first Gulf War in 1991.

B-52 bombers were most recently used in March following a decision by former UK prime minister Sir Keir Starmer to allow the US to use UK bases - including RAF Fairford - for "defensive" strikes on Iranian capabilities.

Conflict was sparked across the Middle East after the US and Israel launched wide-ranging strikes on Iran on 28 February.