Iran arrested the managing director and political editor of a pro-reform daily on Wednesday, with the semi-official Fars news agency saying their detentions were linked to the publication of a letter from a former president about media freedom.
With a presidential election three months away, Iran's clerical leadership appears to be tightening its grip on the media to avoid a repeat of the protests that erupted after the disputed re-election of President Mahmoud Ahmadinejad in 2009.
Fars agency quoted the daily Maghreb's editor, Amir Mousa Kazemi, as saying that the arrests "can be related to the publication of Mohammad Khatami's letter" on Tuesday.
In the letter, the moderate former president, succeeded by Ahmadinejad, said he hoped Maghreb would continue to work alongside the "few remaining independent" publications in the country.
Khatami publicly backed defeated candidate Mirhossein Mousavi during the 2009 presidential election, which reformists said was rigged. Iran denied the accusation and has put Mousavi under house arrest for more than two years, along with fellow opposition leader Mehdi Karoubi.
With Iran's main reform leaders detained, Khatami has sometimes been the voice of the moderate opposition movement. The paper said on its website it had sought his opinion about its work, which resulted in his letter's publication.
ISNA, the Iranian Students' News Agency, said managing director Mohammad Mehdi Emami Nasseri and political editor Alireza Aghaeirad were detained by agents from Tehran prosecutor's office.
Iran's pro-reform publications have often reported on an economy struggling under Western sanctions imposed over Iran's disputed nuclear programme, and feature criticism of Iranian government policies.
Iran arrested dozen of journalists in January over their links to "anti-revolutionary" media. Some of them have been released in recent days.
The Iranian leadership regularly accuses Western governments of trying to foment social unrest through subversive media activities but says that such plans will never succeed.
Many moderate journalists were detained following the mass street protests that were crushed by security forces after the last election.