LONDON, U.K.: British police investigating a suspected terrorist plot linked to an air base used by the U.S. in operations against Iran have arrested a dual British-Iranian national, officials said on October 1.

The 27-year-old man was arrested in London on suspicion of preparing terrorist acts. Police also questioned a 26-year-old British man under caution as part of the investigation.

The arrests follow a major incident near RAF Fairford in western England on September 27. Five British men in their 20s were arrested on suspicion of terrorism and explosives offenses, leading to a large police operation and concern among Western allies.

The five men were later released without charge on police bail. However, counter-terrorism officers said they were examining whether a foreign state was involved.

Prime Minister Andy Burnham said the incident could have links to Iran.

The latest arrest has added to the investigation into what happened near RAF Fairford, a military base that has been used by the U.S. for operations involving Iran.

Police have provided few details about the original incident, which remains largely unexplained. Investigators are examining several possible explanations and trying to establish whether those involved had links to a foreign government.

Britain's counter-terrorism police said the investigation was complex and involved several lines of inquiry.

"The investigation into circumstances surrounding events in Gloucestershire is hugely complex, and our specialist teams are interrogating multiple lines of inquiry," said Vicki Evans, Britain's Senior National Coordinator for Counter Terrorism Policing.

Police said the latest arrest was made in London and that the 27-year-old dual national remained in custody. The second man, aged 26, was questioned under caution but was not arrested.

Specialist counter-terrorism officers are leading the investigation, examining the events in Gloucestershire and possible foreign involvement.

The case comes amid heightened tensions involving Britain, the United States and Iran. RAF Fairford is a strategically important military base and has been used by U.S. forces for long-range military operations.

Authorities have not said what the suspects were allegedly planning or whether the investigation has uncovered evidence directly connecting them to Iran.

Police have also not said whether the latest arrests are directly connected to the five men detained near RAF Fairford on September 27. The earlier suspects were released without charge while the investigation continues.

Counter-terrorism officials have stressed that several possibilities remain under examination as they work to establish what happened and whether a foreign state played any role.