British Prime Minister Andy Burnham said Monday that a suspected plot to attack a U.S.-run air base in England was "almost certainly" directed by Iran's Revolutionary Guard.

He told lawmakers it was highly likely the plan was coordinated in Iran.

He added that Britain will not tolerate such threats on its soil.

The target was RAF Fairford, used by American bombers to strike Iran in the ongoing war.

Police have arrested seven men, all in their 20s.

All have been released on bail and none has been charged.

Six are British nationals and one holds dual U.K.-Iranian citizenship.

On Sept. 27, scores of residents near the base were evacuated.

Armed police and army bomb-disposal experts moved into the rural area.

Police later said they found gasoline in three vans linked to the first five suspects, but no explosives.

Iran has denied involvement.

However, it has said it considers any base used to attack its territory a legitimate target.

Britain summoned the Iranian ambassador on Monday.

He repeated that Tehran was not involved and urged the U.K. to provide evidence.

Britain also added two Iranians to its sanctions list.

This includes the head of counterespionage operations in the Revolutionary Guard.

The Pentagon said the U.S. pulled its bombers from RAF Fairford last week.

They have been redeployed to their home bases.