Donald Trump has warned the five men arrested over a foiled terror attack at RAF Fairford were 'looking to do big damage' to US forces.

The arrests come amid heightened concerns around the threat from hostile states to the UK, with Russia among those that have used proxies to commit crimes on their behalf on British soil.

However, counter-terrorism police are understood to be probing a potential link to Iran.

RAF Fairford, in Gloucestershire, is the US Air Force's command outpost for operations from Europe and has been used for American strikes on Iranian missile sites that have been attacking ships in the Strait of Hormuz.

The base was the subject of a warning from Iran's Revolutionary Guard in July, with the regime warning Britain not to allow US bombers to fly from the base.

The US President praised the UK police response and suggested authorities already had the suspects under investigation. 

He told reporters in Illinois: 'It was fantastic. Working with Britain, it was an amazing job. We had them under investigation. They were looking to do big damage to our fort, and working with the British worked out great. 

'It may have been Scotland Yard, I don't know. We worked with a lot of them. We had them under view for a long time, and we got them. Thank you.'

However, today's arrests are not believed to be part of a pre-planned operation, meaning police were previously unaware of the plot.

It comes as a local farmer was said to have alerted police over the alleged car bomb plot after stumbling upon five 'Middle Eastern-looking, masked' men on the way home from a party.

'I just thought what the hell are they doing… I saw a group of Middle Eastern-looking young guys running off through the trees. Some of them had masks or balaclavas on, and they all scattered ahead of us as we drove back past.

'Some of them ran into the fields, and some of them turned to run towards the air base. We realised this was something pretty serious,' she told the Telegraph.

Responding to Mr Trump's words on Fairford, Wes Steeting said: 'This is my first experience as Defence Secretary in responding live to the president. 

'I'm sure it won't be the last.'

He praised the 'exemplary response' from security services to the incident but refused to comment on the 'underlying motivations' of those arrested.

Speaking at a Labour Party conference fringe event in Liverpool, he said it was 'an example of what they do day in, day out, at all hours and all across the world, to keep us safe, so often going unnoticed and unsung, but we are glad that they do and we are glad that they are there to defend us'.