By Parisa Hafezi and Dominic Evans
TEHRAN (Reuters) - Iran detained more than 100 reformers including the brother of a former president, a leading reformer said on Sunday, after violent street protests in Tehran against the re-election of President Mahmoud Ahmadinejad.
Supporters of defeated moderate candidate Mirhossein Mousavi, who has dismissed Ahmadinejad's election victory to a second term as a "dangerous charade," gathered in the centre of the capital again on Sunday and chanted his name.
The world's fifth biggest oil exporter saw the most widespread protests on Saturday since Iran's 1979 Islamic Revolution, and residents in five other cities said people had taken to the streets to support Mousavi.
Hardliner Ahmadinejad was planning celebrations in the capital later on Sunday. His unexpectedly overwhelming victory and its violent aftermath raised fresh questions about the direction of Iranian policies at a time when U.S. President Barack Obama wants to improve relations with Iran.
Iranian and Western analysts said Ahmadinejad's victory would disappoint Western powers aiming to convince Iran to halt a nuclear programme they suspect is aimed at making bombs. Obama had urged Iran's leadership "to unclench its fist."
Mohammad Ali Abtahi, who served as a vice president under Mohammad Khatami, told Reuters the former president's brother Mohammad Reza Khatami was one of more than 100 members of Iran's biggest reformist party Mosharekat who were held on Saturday.
A judiciary spokesman said the reformers were summoned and warned not to increase tension. He said they were then released.
Mousavi's wife, Zahra Rahnavard, denied reports that her husband himself had been detained or put under house arrest.
"He is following the issue of the election. He says he is with the people and beside them," said Rahnavard, who campaigned actively alongside her husband during a campaign which drew tens of thousands of supporters onto the streets of Tehran.
"TURBULENCE" IN IRAN
Mousavi has rejected Ahmadinejad's victory, which he complained was marred by violations and vote-rigging and said would "jeopardise the pillars of the Islamic Republic and will establish tyranny."
Interior Ministry officials have rejected accusations of fraud and Supreme Leader Ayatollah Ali Khamenei has called on Iranians to back their president.
The anti-Ahmadinejad camp was "taken by surprise and is scrambling for a plan," according to Trita Parsi, director of the Washington-based National Iranian American Council.
"Increasingly, given their failure to get Khamenei to intervene, their only option seems to be to directly challenge -- or threaten to challenge -- the supreme leader," he wrote.
A senior Western diplomat in Tehran said he believed the street unrest would soon end. "It will not be allowed to spread. They will apply all their force to subdue it," he said.
But while Ahmadinejad had won, his re-election battle had exposed a polarising power struggle between radicals and moderate conservatives which in the long term could have an impact on the stability of the Islamic Republic, he said.
"There is turbulence in the whole system," the diplomat said.
Protests also broke out on Saturday in the cities of Tabriz, Orumieh, Hamedan and Rasht, where crowds chanted for Mousavi.
In Isfahan, police intervened and made arrests after students at Sanati University set equipment and furniture on fire, a witness told Reuters. In Tehran police beat protesters on Saturday with batons as they spread out across the capital. Small fires burnt at roadsides.
Though the protests were small compared to the mass demonstrations that led to the 1979 Islamic revolution, they were the most widespread in the city since then.
Ahmadinejad, in a televised address to the nation, said the election had been "free and healthy."
U.S. Secretary of State Hillary Clinton said the United States was monitoring the outcome of the election closely and hoped the result reflected the will of the Iranian people.
A senior State Department official insisted Obama's decision to engage Iran was not based on any particular electoral outcome and the path ahead would be hard no matter who won.
"There are a lot of different factions and mixed views on the idea of engaging the Great Satan (Washington)," said the official, speaking before the official results came out.
"We are going to engage the Iranian government whether it is led by one faction or the other," he added.
(Additional reporting by Fredrik Dahl; editing by Peter Millership)
