An Iranian diplomat with ties to the reformist camp has been arrested following "a misunderstanding", Foreign Minister Alki Akbar Salehi was quoted as saying Thursday 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 the date or motives of Asadi's arrest.
Asadi is "a talented expert and we have seen him do nothing other than defend the nation's interest", Salehi added.
Bagher Asadi was the Islamic republic's ambassador to the United Nations during the 1997-2005 presidency of reformist Mohammad Khatami.
In January 2004, Asadi had published an op-ed in the New York Times in which he criticised the conservative camp, whose candidate Ahmadinejad defeated Khatami 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 then.
"Until Iranians develop a solid base for a robust, dynamic civil society, we will not be able to make political achievements irreversible."
Ahmadinejad's reelection in 2009 was condemned as fraudulent by the reformist camp, whose candidates Mir Hossein Moussavi and Mehdi Karoubi have been under house arrest for more than two years.
Intelligence Minister Heydar Moslehi on Thursday warned ex-presidents Akbar Hashemi Rafsanjani and Khatami, without naming them, over 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.
His comment was seen as a thinly-veiled warning to Khatami.