Security forces arrested several supporters of moderate presidential candidate Hassan Rowhani in Iran's June 14 election after pictures of detained opposition leader Mir Hossein Mousavi were displayed at a meeting, websites reported Sunday.
Opposition website Kaleme.com reported seven arrests of participants in a ceremony in the Jamaran mosque in northern Tehran on Saturday, with relatives saying "they were taken to Tehran's Evin prison".
Conservative website nasimonline.ir and alef.ir also reported the arrests and showed pictures of former premier Mousavi being held by some people at the gathering.
Mousavi and reformist Mehdi Karroubi were defeated by Mahmoud Ahmadinejad in the 2009 presidential election, and alleged fraud when the incumbent was re-elected.
Their claim led to deadly street violence and a bloody crackdown on dissent by the regime.
Both Mousavi and Karroubi have now been under house arrest for more than two years.
Media also reported that banners reading "Death to the dictator", "Political prisoners must released" and "The prime minister of the Imam (Ayatollah Ruhollah Khomeini) must be freed," were seen at the meeting.
Mousavi was prime minister, a now defunct post under the new constitution, from 1981 to 1989 during Khomeini's rule.
Police issued a warning to candidates on Sunday after the Jamaran mosque incident.
"One of the candidates' obligations is not to follow the leaders of the sedition in 2009," national police chief General Esmaeel Ahmadi Moghaddam was quoted by the ISNA news agency as saying.
"What occurred may not be linked to the candidate, but some people may have wanted to take advantage of the situation.
"The police will carry out its duty and confront those who seek to take anti-revolutionary actions," he added.
Earlier, a spokesman for Rowhani's campaign did not confirm the arrests to AFP, saying that "some people tried to disrupt the meeting".
Rowhani's office issued a statement condemning "any improper action" and asking everyone to respect the law and remain calm.
The moderate Rowhani is one of eight candidates approved by constitutional watchdog the Guardians Council to stand for president on June 14.
He is considered close to former reformist president Mohammad Khatami (1997-2005), and was Iran's chief nuclear negotiator between 2003 and 2005.
Although reformists are weak politically, Rowhani is hoping to harvest their votes along with those who would have voted for the former pragmatic president, Akbar Hashemi Rafsanjani.
Rafsanjani was disqualified from standing by the Guardians Council.