LONDON (AP) — Two men were charged Tuesday with national security offenses over a suspected plot against RAF Fairford, a US-run military air base in England, police and prosecutors said.

British nationals Mohmed Ahmad Abdulkarim and Nouman Essghir, both aged 24 and from London, were charged under the National Security Act, the Crown Prosecution Service said. They are due to appear in court later Tuesday.

Abdulkarim is charged with assisting Iran’s intelligence service and Essghir with entering a prohibited place for a purpose prejudicial to the UK.

RAF Fairford, in western England, has been used by American bombers to strike Iran during this year’s war.

Essghir was arrested outside the base on Sept. 27, when armed police officers and army bomb-disposal experts swarmed the rural area. Scores of residents were evacuated from their homes as police and army bomb-disposal experts searched for explosives.

Police later said they had found a quantity of an accelerant — gasoline — in vans at the scene, but no explosives.

Essghir was initially released on bail before being re-arrested last week. Abdulkarim was arrested in the past week.

Six other men have been arrested and released on bail as investigations continue.

British authorities have linked Tehran to the incident, which led the US to pull its bombers from RAF Fairford.

Prime Minister Andy Burnham said that the apparent plot was “almost certainly” directed by Iran’s Revolutionary Guard.

Iran has denied involvement, although it has previously said that it considers any base used to attack its territory a legitimate target.

Earlier this month, the head of Britain’s MI5 spy agency warned that both Iran and Russia were expanding their attacks against the UK, and that the RAF Fairford incident was not unique.

Ken McCallum, who leads the UK’s domestic security service, said Tehran is seeking to intensify its attacks in Britain beyond the traditional targets of Iranians opposed to the country’s Islamic authorities.

He said more than 50 people have been arrested over Iran-linked plots in the past year.

“We have seen a range of incidents in recent months that we believe have been directed by the Iranian state, and as the director general of MI5 said just the other week, we are working together to intervene, identify and respond to that threat,” said Assistant Commissioner Laurence Taylor, the head of National Counter Terrorism Policing in the UK.