By Parisa Hafezi and Dominic Evans
TEHRAN (Reuters) - More than 100 reformists were arrested on Saturday night after President Mahmoud Ahmadinejad's presidential election victory led to violent street clashes in Tehran, leading reformist Mohammad Ali Abtahi said on Sunday.
In a rare challenge to authorities, thousands scuffled with police on Saturday after Ahmadinejad's disputed defeat of reformist candidate Mirhossein Mousavi sparked the biggest protests in Tehran since the 1979 Islamic revolution.
Iranian and Western analysts said Ahmadinejad's re-election disappointed Western powers aiming to persuade the world's fifth-biggest oil exporting country to halt a nuclear programme they suspect is aimed at making bombs which Iran denies.
Tehran streets were generally quiet early on Sunday with one opposition gathering reported. Ahmadinejad was expected to make several public appearances during the day, including a victory speech to supporters.
A judiciary spokesman said the reformists had not been arrested but were summoned and "warned not to increase tension." They were later released, he told Reuters.
The arrested reformists were members of Iran's leading reformist party Mosharekat and included Mohammad Reza Khatami the brother of former President Mohammad Khatami.
Abtahi, a former vice-president, told Reuters: "They were taken from their homes last night." He said more arrests were expected.
The election result 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. Obama has urged the leadership to "unclench its fist."
Supreme Leader Ayatollah Ali Khamenei told Iranians to respect Ahmadinejad's victory, which upset expectations that Mousavi might win the contest.
Interior Minister Sadeq Mahsouli, an Ahmadinejad ally, declared the president had been re-elected with 62.6 percent of the vote, against 33.7 percent for Mousavi.
Mousavi complained of violations and vote-rigging -- allegations rejected by Interior Ministry officials.
"I'm warning I will not surrender to this dangerous charade. The result of such performance by some officials will jeopardise the pillars of the Islamic Republic and will establish tyranny," Mousavi said in a statement made available to Reuters.
POLICE BEAT PROTESTERS
After the result was announced, thousands of his supporters took to the streets, some chanting, "What happened to our vote?" Others shouted anti-Ahmadinejad slogans. "We are Iranians too," and "Mousavi is our president," they shouted.
Police beat protesters with batons as they spread out across the capital. Small fires burnt at roadsides.
Although the protests were small compared with the mass demonstrations that led to the 1979 Islamic revolution, they were the most widespread in the city since then.
Khamenei, Iran's top authority, told defeated candidates and their supporters to avoid "provocative behaviour."
"The chosen and respected president is the president of all the Iranian nation and everyone, including yesterday's competitors, must unanimously support and help him," Khamenei said in a statement read on state television.
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.
Late on Friday, before official results emerged, Mousavi had claimed to be the "definite winner." He said many people had been unable to vote and ballot papers were lacking.
Ahmadinejad draws most of his support from rural areas and poorer big city neighbourhoods. Mousavi enjoys strong backing in wealthier urban centres, especially among women and the young.
(Editing by Peter Millership)
