An Iranian diplomat with ties to the reformist camp has been arrested following "a misunderstanding", Foreign Minister Ali Akbar Salehi was quoted as saying by the Isna news agency.
Bagher Asadi's detention comes weeks ahead of the June 14 presidential election, the first since the wave of protests that followed the 2009 poll that saw Mahmoud Ahmadinejad defeat reformist candidates.
"We hope that the misunderstanding over Mr Asadi, who is a senior and respected employee of the foreign ministry, will be resolved and that he will be freed," Salehi said.
The foreign minister did not specify when Asadi was arrested or why.
Asadi is "a talented expert and we have seen him do nothing other than defend the nation's interest", Salehi added.
Asadi was a senior diplomat at the Islamic republic's United Nations representation from 1997 until 2002 covering most of the presidency of reformist Mohammad Khatami 1997-2005, according to reformist websites.
In January 2004, Asadi had an op-ed published in the New York Times in which he criticised the conservative camp, whose candidate Ahmadinejad defeated Akbar Hashemi Rafsanjani the following year.
"The conservatives' blatant disdain for human rights and republican aspects of governance, among other things, would inevitably invite outside censure and further complicate an already tenuous relationship," he wrote.
"Until Iranians develop a solid base for a robust, dynamic civil society, we will not be able to make political achievements irreversible."
Ahmadinejad's re-election in 2009 was condemned as fraudulent by the reformist camp, whose candidates Mir Hossein Mousavi and Mehdi Karroubi have been under house arrest for more than two years.
Intelligence Minister Heydar Moslehi yesterday warned ex-presidents Hashemi Rafsanjani and Khatami, without naming them, about their alleged role in the protest movement.
"One of the leaders of the plot, who was not put under house arrest like the other two for various reasons, should not fool himself and think that the revolutionary power has forgotten the role he played in the plot," he said in a speech in the northern city of Qom.
Moslehi's comment was seen as a thinly veiled warning to Khatami.
