A suspected terror plot against an RAF base used by American forces “clearly involves the hand of a foreign actor”, US Secretary of State Marco Rubio has claimed, but refused to provide further details.
In a TV interview, the top diplomat mentioned Iran by name, pointing out it had threatened to attack US interests, but did not directly blame it for the weekend incident.
Tehran has strongly denied any involvement, calling claims to the contrary “unfounded and malicious speculations”.
Rubio described events that unfolded near RAF Fairford in Gloucestershire as a “very serious situation” and thanked the British authorities for their response, saying they had been “very cooperative and very helpful”.
He also noted “a lot of people are disturbed” following the release of five suspects on bail, who had been arrested in connection with the alleged plot.
US President Trump had earlier said he was “surprised” the group had been freed.
The five men, all British nationals in their 20s, were detained on suspicion of explosives offences and terrorism on Sunday after three vans were found near RAF Fairford in Gloucestershire, which has been used by the US military to carry out strikes against Iran.
Residents evacuated from about 85 households were able to return home on Monday, but a cordon remained in place around the vehicles as counter terrorism officers continue to examine the scene.
It is understood that the material found was not viable explosives, but police have said the investigation is continuing.
Speaking to Fox News, Rubio said: “I have to be careful. There are some things I cannot say on the air for a lot of different reasons.
“Suffice it to say that what happened, what almost happened, what could have happened in the UK over the weekend is a very serious situation.
“It’s one that clearly involves the hand of a foreign actor. I won’t get into great detail about that yet.
“I do want to thank the authorities in the United Kingdom who have been very cooperative and on top of it.
“I know a lot of people are disturbed by the news that some of these people have been released on bail, as some of the people are being investigated, and obviously we’re engaging with them on all of that.
“Beyond that, I would argue that they’ve been very cooperative and very helpful on something that’s a very serious incident.”
Rubio went on: “I think it ties us to the reality here, and that is we are dealing with elements in the world, and in the case of Iran, for example, who have openly threatened to attack American interests globally.
“We’re going to always take that very seriously. There’ll be repercussions for that if it ever were to happen or even attempted.
“But what happened this weekend could have been and was, I think, a very serious threat. I want to thank the UK for their cooperation and their help on it.
“There’s a lot more news that’ll come out on this in the days to come, but there’s only so much I can say right now at this point about it, other than this was a very serious thing and it was responded to appropriately.”
Earlier, the head of UK Counter Terrorism Policing, Assistant Commissioner Laurence Taylor, acknowledged speculation on whether Iran was behind the incident and said the force was considering “every possible angle”.
In a statement outside New Scotland Yard on Monday, Taylor said he knew there was “significant interest in whether the current geopolitical context has a bearing on this incident”.
“At Counter Terrorism Policing, we are working within this context every single day and, at this stage, we are keeping an open mind in this investigation,” he continued.
“We have, as you would expect, ensured that our protective security advice and posture remain commensurate to the threat.
“But be assured, we are considering this from every possible angle, including that this may be actively committed by proxies or individuals either knowingly or unknowingly working on behalf of a foreign state.”
Iran, and other hostile states including Russia, have been known to use criminal proxies to carry out crimes on their behalf on UK soil.
The country’s London embassy earlier said it “categorically rejects and strongly condemns the recent unfounded and malicious speculations” of Iranian involvement.
The five suspects are a 24-year-old from Camden, north London; three men aged 23, 24 and 25 from Westminster, central London, and one aged 24 from Willesden, north-west London.
Taylor said the men were released on bail under “stringent conditions” on Monday but “absolutely remain under investigation as we explore multiple lines of inquiry”.
Prime Minister Andy Burnham chaired a Cobra meeting on Monday.
After the meeting, Defence Secretary Wes Streeting said the decisions around bail were operational matters for the police and prosecutors, and the investigation remained ongoing.
Speaking in the White House on Monday, Trump said: “I will tell you, I would have said ‘Don’t let them have bail’. I’m surprised that they released them. I wouldn’t have done that.”
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