Two men have been re-arrested after an incident near RAF Fairford last month, counter-terrorism police have said.
A 24-year-old UK national, and a 25-year-old dual UK-Iranian national, are being held on suspicion of assisting a foreign intelligence service under Section 3 of the National Security Act 2023, with police saying the investigation relates to Iran.
Police had been alerted to three suspicious vehicles near the US airbase in Gloucestershire in the early hours of 27 September - a major incident was subsequently declared and dozens of homes evacuated.
Seven men in total have been arrested as part of the counter-terror police investigation.
Gloucestershire Police said it had received a call about "three suspicious vehicles" travelling towards RAF Fairford at 00:45 BST on 27 September.
A bomb disposal team was deployed to the village to examine a number of vehicles.
Petrol was found in three vans near the airbase and five men were arrested.
They had been initially arrested on suspicion of committing offences under the Explosives Act and then further arrested on suspicion of preparation of a terrorist act.
Police later said they did not find "improvised explosive devices".
The re-arrests announced on Tuesday relate to a 24-year-old man who was initially arrested on 27 September near the base and a 25-year-old who was arrested on suspicion of preparation of terrorist acts days later on 1 October in the borough of Westminster.
The other five men - who also include a 22-year-old British national arrested in Westminster on 6 October - remain on police bail.
The head of National Counter Terrorism Policing, Assistant Commissioner Laurence Taylor said: "This is very much a live investigation, and our evidence gathering continues, but at this time our position remains the same; we consider it highly likely that there is Iranian state involvement.
"Our investigators are continuing to examine what that level of involvement was and the ambition behind it."
The officer added that national security investigations can take time to progress due to their sensitive nature.
"Our specialist teams have been working tirelessly to interrogate the many lines of enquiry involved in this hugely complex investigation," he said.