GENEVA - The United Nations human rights office called on Tuesday for the immediate release of prominent activists and journalists it said had been arrested or intimidated as part of an apparent clampdown on critical voices ahead of next year's presidential election.Spokesman Rupert Colville cited among others the cases of Ali Akbar Javanfekr, press adviser to President Mahmoud Ahmadinejad and head of the state-run IRNA news agency, jailed for six months for insulting the Supreme Leader, and Reuters Bureau Chief Parisa Hafezi charged with spreading lies and propaganda."It's certainly a clampdown, it's a large number of people, quite prominent people just in the past two weeks. There does seem to be some political linkage possibly to the forthcoming elections," Colville told a news briefing.Colville said he was particularly concerned about the Sept. 29 arrest of human rights lawyer Mohammad Ali Dadkhah, who had been sentenced to nine years in prison for "membership of an association seeking to overthrow the government and propaganda against the system." Colville also referred to the detention last month of Faezeh Hashemi and Mehdi Hashemi Rafsanjani, the daughter and son of Akbar Hashemi Rafsanjani, former President of Iran.President Mahmoud Ahmadinejad was first elected in 2005 and is due to step down next year when new polls are held. His reelection in 2009 resulted in demonstrations and accusations of electoral fraud that rocked the country.