Iran has confirmed it is holding a US citizen, the first American detained in the Islamic Republic during the Trump presidency.
Former US Navy member Michael R White, 46, was arrested “some time ago” and is being held at an Iranian prison, the foreign ministry said.
Spokesman Bahram Ghasemi said US officials had immediately been made aware of the arrest.
Mr White’s mother told US media her son has been missing in Iran since July.
Joanne White told the New York Times he had gone to visit a girlfriend, and was due to return via Dubai on 27 July.
She said she did not know what charges he faces, and that he had previously visited Iran “five or six times”.
“All I know is that he is alive and they were putting in a request for a consular visit by the Swiss,” she said.
The US and Iran do not maintain diplomatic relations, and communications between the two nations are passed along by Swiss diplomats.
Iranian officials said Mr White was detained in the city of Mashhad, in the north-east of the country.
A Department of State spokesperson told the BBC: “We are aware of reports of the detention of a US citizen in Iran.
“We have no higher priority than the safety and security of US citizens abroad.
“Due to privacy considerations, we have no additional information to provide at this time.”
Mr White is originally from Imperial Beach, California, 14 miles (22km) south of San Diego.
His family say he suffers from acute asthma and shortly before his latest visit he underwent chemotherapy for a neck tumour.
Mr White’s arrest was reported on Monday by the blog, Iranwire.
It was based on the account of a former Iranian prisoner who said he met Mr White at Vakilabad Prison in Mashhad in October.
Ivar Farhadi, a cyber-activist who spoke to CBS News, said Mr White had been arrested while preparing to fly to Turkey to marry his girlfriend.
At least three other American citizens are being held in Iran.
Another US man has been missing in Iran for over a decade.