The U.K. has said it had charged a man with an offense of assisting a “foreign intelligence service” over an incident at a military base used by the U.S. for strikes on Iran.

Mohmed Abdulkarim, 24, has been charged under the country’s National Security Act “following an incident involving RAF Fairford,” an air base in the west of England, prosecutors announced on Tuesday.

Between Aug. 31 and Sept. 28, Abdulkarim is alleged to have engaged in “conduct that would likely materially assist a foreign intelligence service in carrying out U.K.-related activities”, the Crown Prosecution Service added. The foreign country was not named.

Prosecutors also charged 24-year-old Nouman Essghir with “entering a prohibited place for a purpose prejudicial to the UK”.

The men are due to appear in court in London on Tuesday.

Five people were arrested on suspicion of explosives and terrorism offenses near RAF Fairford on Sept. 28. The base had been used as the U.S. Air Force’s command outpost for operations from Europe and for American strikes on Iranian missile sites.

Announcing the charges, Frank Ferguson, a chief prosecutor for the Crown Prosecution Service’s Special Crime and Counter Terrorism Division, said that they followed “a Counter Terrorism Policing investigation into a high-profile incident involving RAF Fairford.”

“We will continue to work closely with our partners as this complex investigation continues,” he said.

After the arrests, U.S. President Donald Trump said the U.S. had moved its long-range bombers out of the U.K. in response to a threat “linked to Iran.”

Prime Minister Andy Burnham told lawmakers earlier this month that the incident was “highly likely to have been coordinated in Iran, almost certainly directed by Iran’s Islamic Revolutionary Guard.”

Over the summer, Iran’s Revolutionary Guard warned it saw any military base involved in launching airstrikes on Iran as a legitimate target.

Tehran denied any involvement in the incident at RAF Fairford.