The men were detained early on Sunday after three vans were seen near RAF Fairford, a UK-owned base that has been used by American bombers during decades of conflicts in the Middle East.
Investigators have not concluded whether the incident is a state-backed attack.
They are investigating a possible link to Iran, Russia or non-state-backed militant groups.
The five suspects, who have not been named, were initially held over suspected explosives offences, and later also arrested on suspicion of preparing an act of terrorism.
Police said the men were all British nationals from London and in their 20s.
They can be held in custody for up to 14 days before they must be charged or released.
Residents were evacuated from 85 homes in the village of Whelford near the base on Sunday and army bomb-disposal experts used a robot to examine three white vans.
The villagers had not been able to go home as of Monday morning, and the vans had not yet been moved.
US President Donald Trump said the suspects had been detained following co-operation between the US and Britain, and had been "under view" for some time.
Police, however, said the arrests were triggered by a late-night call about "suspicious vehicles" near the base.
Prime Minister Andy Burnham said the incident was "deeply concerning" and the government would "always take every step necessary" to protect people.
Defence Secretary Wes Streeting declined to give details of the operation, but told Time Radio that "it was a proud moment" that Trump had recognised "the work that our police and intelligence services do every day".
The arrests come at a time of heightened tensions around the threat from hostile states, with British intelligence services saying Russia and Iran have both used proxies to commit crimes on British soil.
In March, officials said the number of national security cases involving activity by hostile states, including Iran, increased 50 per cent in the six months to December 2025.
Britain did not join the US-Israeli war on Iran that began February 28 and initially denied Trump's request to use bases in the UK to strike Iran.
But then-prime minister Keir Starmer agreed in March to let the US use bases in Britain for what he called "defensive" operations against Iran's missiles and their launch sites following Iranian attacks on UK interests and Britain's allies in the Gulf.
American B-1 and B-52 bombers have taken off from Fairford, 160km west of London, for operations during the Iran conflict.
Iran has said it considers any base used to attack its territory a legitimate target.
British security officials say proxies linked to Iran have been behind a string of arson and sabotage attempts in the UK and other countries, many of them targeting the Jewish community.
They have previously warned that Tehran could expand its targets in the UK if conflicts in the Middle East continue.
British Foreign Secretary Ed Miliband met Iran's Foreign Minister Abbas Araghchi at the United Nations in New York last week and told him that "Britain will not tolerate intimidation, threats or hostile activity on UK soil".
The US Air Force said its personnel based at RAF Fairford "remain vigilant", but "for operational security reasons we will not discuss specific force protection measures".
Trump said authorities had the suspects "under view for a long time and we got them".
"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," he told reporters in Chicago on Sunday.
