The 25-year-old man was arrested in London, and police searched two properties in the U.K. capital, Counter Terrorism Policing said.
A dual U.K.-Iranian national who was arrested earlier this week on suspicion of plotting a terror attack following a security incident at the U.S.-run RAF Fairford air base in England that British authorities have linked to Tehran was released on bail Saturday.
The 25-year-old man was arrested in London on Thursday, and police have searched two properties in the U.K. capital, Counter Terrorism Policing said in a statement.
On Saturday, Counter Terrorism Policing announced that the man had been released on bail.
"The investigation into the circumstances surrounding events in Gloucestershire is continuing," the agency said in a new statement.
British police also initially reported that a second 26-year-old British national had been interviewed by investigators "under caution," meaning the interview was recorded and could be used in future prosecutions. However, they later disclosed that this was "not correct and has been removed" from their statement.
On Sept. 27, five men, all British nationals in their 20s and from London, were also arrested on suspicion of explosives and terror offenses close to the RAF Fairford air base, which has been used by American bombers to strike Iran. The suspects have also since been released on bail.
Their quick release drew criticism from President Trump and U.S. Secretary of State Marco Rubio. But it also prompted questions in the U.K. as to whether the authorities had overreacted.
Police say they found a quantity of an accelerant – gasoline – in three vans linked to the five suspects, but no explosives.
Vicki Evans, the senior national coordinator for counter terrorism policing, said the investigation "is hugely complex, and our specialist teams are interrogating multiple lines of inquiry."
"As we've made clear, we're looking at all possible angles - including possible foreign state involvement," she said.
Prime Minister Andy Burnham said the U.K. sees "strong indications" that Iran played a part in the incident. Iran denies involvement.
"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, and of course we are working closely with our colleagues in the United States of America," the prime minister told the BBC.
The base 100 miles west of London has been used by American bombers during decades of conflicts in the Middle East, including this year's war with Iran.
Iranian authorities have warned that any bases used to attack the country would be considered legitimate targets, but the Iranian Embassy in London said in a statement shared Monday on social media that the regime "categorically rejects and strongly condemns the recent unfounded and malicious speculations published by some British individuals and media outlets attempting to link Iran" to the incident.
Burnham said authorities have the investigation under "the strongest grip and the closest control," and British officials had been "talking to counterparts in the United States all week to explain what is happening here, how things are being done."
U.K. officials say proxies linked to Iran have been behind a string of arsons and other attacks in Britain and other countries, many of them targeting the Jewish community and intended to sow fear. They have previously warned that Tehran could expand its targets in the U.K. if conflicts in the Middle East continue.