A dual British-Iranian citizen has been arrested in connection with the attempted terrorist attack at the RAF Fairford base.

This is the sixth arrest in connection with the incident, after five men were arrested under the Explosives Act and on suspicion of preparing a terrorist act after three suspicious vans were spotted traveling toward the Gloucestershire airbase in the early hours of Sunday morning.

The dual citizen is suspected of plotting to carry out a terrorist attack. Another British national has also been questioned.

Senior national coordinator for counter terrorism policing for the Metropolitan Police Vicki Evan stated: "We’re looking at all possible angles - including possible foreign state involvement."

British Prime Minister Andy Burnham said Wednesday that there are “strong indications" Iran was involved in the plot to attack the RAF base.

“There are strong indications that Iran played a part in what happened over the weekend at RAF Fairford, but of course it remains an ongoing, complex, and serious police investigation," Burnham told BBC News. “And of course, we are working closely with our colleagues in the United States of America. So it’s ongoing."

Burnham said he had convened the government’s Cobra emergency committee while in Liverpool and insisted that authorities were fully addressing the situation. “We are on top of it in every possible way imaginable," he said.

“We will say more in due course, but we can confirm our belief that we believe Iran to have played a part," he added. Asked why he believed Iran was involved, Burnham said, “Well I can’t go into all of those details, but obviously I wouldn’t say it lightly."

The five suspects, all London residents in their 20s, were detained in the Gloucestershire countryside near RAF Fairford after a local woman reported seeing several vans and masked men while driving home.

They were initially arrested on suspicion of explosives offenses and later detained on suspicion of preparing acts of terrorism. All five were released on police bail Monday following examinations of items found in the vans and searches at addresses associated with them in London.