Britain's Foreign Secretary Ed Miliband summoned Iran's ambassador to London on Monday following an incident last month at RAF Fairford, a Gloucestershire airbase, to deliver a formal diplomatic protest over alleged Iranian-directed security threats on British soil.

Prime Minister Andy Burnham told Parliament that the incident on September 27 was "almost certainly directed by Iran's Islamic Revolutionary Guard." A large police operation that morning responded to three suspicious vehicles near the base. Dozens of homes in the nearby village of Whelford were evacuated and a cordon placed around the site. Seven men, all in their 20s, were arrested and later released on bail. No charges have been filed.

Miliband stated that Iran's "continued attempts" to undermine UK security "through its criminal networks, proxy groups and state-backed malign activity is unacceptable." The UK Foreign Office sanctioned two Iranians, including the head of Tehran's counterespionage operations, with both men subject to travel bans and asset freezes. Burnham indicated further sanctions could follow.

Iran's ambassador Seyed Ali Mousavi denied Tehran's involvement and said the country was willing to cooperate with British authorities.

The UK joined 28 other nations including the US, Canada, Australia, France and Germany in issuing a joint statement condemning Iran "in the strongest terms" for "lethal plotting, arson, sabotage, cyber-attacks, and other hybrid activities." The statement recognized Britain's attribution of Iranian involvement at RAF Fairford.

RAF Fairford has hosted US Air Force operations for decades. In recent months, the US flew B-1 and B-52 bombers from the base for defensive operations in the Middle East after Britain approved their use. Last week, the US withdrew approximately a dozen B-1 bombers from the base back to American soil. Downing Street confirmed the airbase remains safe.

In July, Iran stated that "any base used for aggression against Iranian territory constitutes a legitimate target for our forces."

Home Secretary Shabana Mahmood was expected to provide an update to Parliament on the RAF Fairford incident.