Iranian journalist and translator Bahman Darolshafayi, a dual Iranian-British national and former BBC journalist, has been arrested in Tehran.
Authorities had not announced the reason for Darolshafayi's arrest on February 3.
The opposition website Kalame said Darolshafayi was arrested at his Tehran home by security forces who did not identify their affiliation. They also did not say where they were taking Darolshafayi.
Sources told RFE/RL that Darolshafayi had been interrogated repeatedly by Iranian security officials in recent months.
Darolshafayi lived in London but returned to Tehran about two years ago.
One source said Darolshafayi's Gmail account was hacked recently. Pro-government forces in Iran have been accused in the past of hacking into the e-mail and social-media accounts of journalists and political activists to extract information that has, at times, been used in interrogations.
Darolshafayi worked for about five years with the Persian service of the BBC, which has been accused of spreading lies by Iranian hard-liners. He has also been affiliated with moderate and pro-reform Iranian dailies, including Hamshahri and Sharq.
In recent months, Darolshafayi had mainly been doing translation work. He also has published several books.
Darolshafayi also supported the Green opposition movement that was brutally repressed in 2009. Several of his relatives were arrested in the crackdown that followed the disputed reelection of Iran's former President Mahmud Ahmadinejad.
He has posted information on social-media sites about human rights abuses and the plight of political prisoners in Iran.
The cover photo of his personal Facebook page is an image of Iranian opposition figure Mir Hossein Musavi, who has been under house arrest, along with his wife, university professor Zahra Rahnavard, and reformist cleric Mehdi Karrubi, since February 2011.
Darolshafayi's detention is one of several recent arrests of journalists ahead of elections in February for the parliament and the Assembly of Experts -- a group that could choose Iran's next supreme leader.
Other journalists have been arrested by the intelligence branch of the powerful Islamic Revolutionary Guards Corps (IRGC).
In London, The Guardian newspaper suggested that Darolshafayi's arrest could be an attempt by Iranian hard-liners to undermine an upcoming visit to London by Iranian Foreign Minister Mohammad Javad Zarif.
"The awkward timing of the arrest suggests that hard-liners, who dominate the judiciary and the intelligence apparatus, may be seeking to undermine Zarif and the moderate faction in control of the government as the Iranian foreign minister visits the U.K.," the British newspaper said.
Iran is routinely criticized by media watchdogs for detaining and jailing journalists. Reporters Without Borders ranked Iran 173 out of 180 countries in its 2015 Press Freedom Index.