By Parisa Hafezi and Fredrik Dahl
TEHRAN (Reuters) - Tens of thousands of Iranians chanted support for Mirhossein Mousavi in Tehran Monday after a presidential election they say was stolen from him and handed to the hardline incumbent, Mahmoud Ahmadinejad.
Shouting "Allahu Akbar" (God is greatest), they converged on Revolution Square, where Mousavi was expected to call for calm after two days of the capital's most violent unrest in years.
"Mousavi, take back our votes," the marchers chanted as they waited for an appearance by Mousavi and other pro-reform leaders who back his call for Friday's election result to be overturned.
Stick-wielding men on motorcycles scuffled with some of the marchers, who wore Mousavi's green campaign colours.
The gathering, which took place in defiance of an Interior Ministry ban, was a reply to Ahmadinejad's government-organised victory rally that also drew vast crowds Sunday.
In Washington, U.S. pollsters said a survey they had taken three weeks before the vote showed Ahmadinejad leading by a 2-to-1 ratio, greater than the declared election results.
The poll showed his victory might reflect the will of the people and not widespread fraud, pollsters Ken Ballen and Patrick Doherty said in a column in the Washington Post.
The disputed election has dismayed Western powers trying to induce the world's fifth-biggest oil exporter to curb nuclear work they suspect is for bomb-making, a charge Iran denies.
The European Union increased pressure on Iran to agree to opposition demands to investigate Ahmadinejad's landslide election victory and halt a crackdown on protesters.
France, Germany and Britain led the EU campaign to persuade Iran to clarify the election results despite no sign of new pressure from the United States, their partner at talks intended to ensure Tehran does not develop nuclear weapons.
In Paris, Foreign Ministry spokesman Eric Chevallier said Iran's ambassador had been summoned to hear French concerns over "the brutal repression of peaceful protests and the repeated attacks on the liberty of the press and freedom of speech."
Britain said it was worried that events in Iran might affect any future international engagement with its government.
"The implications are not yet clear," said British Foreign Secretary David Miliband. "What we know is that there has been no Iranian response to the outreach that has been made by the international community, including the United States."
U.S. leaders have reacted cautiously, in the hope of keeping alive President Barack Obama's strategy of engagement with Iran.
The protests over Ahmadinejad's re-election are the sharpest display of discontent in the Islamic Republic for a decade -- and have drawn wider support than the student unrest of 1999.
"I just want to show the president that we are not bandits," said Maryam Sedaghati, a pro-Mousavi demonstrator in her 20s wearing a green headscarf. "I want my vote back."
A retired 61-year-old teacher who gave his name only as Ali, said the rally recalled the 1979 Islamic revolution. "We used to protest against the Shah in this street. I'm so sorry that now to preserve our rights we have to walk the same street."
Mousavi has asked the watchdog Guardian Council to annul the result, citing irregularities. The Interior Ministry and the president have rejected charges of fraud.
Supreme Leader Ayatollah Ali Khamenei, who has upheld the election result, met Mousavi Sunday and told him to pursue his complaints "calmly and legally," state television said.
KHATAMI SPEAKS OUT FOR MOUSAVI
Iran's reformist former president, Mohammad Khatami, assailed the authorities for denying permission for the pro-Mousavi rally and said the election had dented public trust.
The 12-man Guardian Council, whose chairman, Ayatollah Ahmad Jannati, endorsed Ahmadinejad before the vote, said it would rule within 10 days on two official complaints it had received from Mousavi and another losing candidate, Mohsen Rezaie.
The council vets election candidates and must formally approve results for the outcome to stand.
Ebrahim Yazdi, leader of the banned opposition Freedom Movement, said Ahmadinejad's attacks on his opponents had opened a "Pandora's box" of divisions within the establishment and between the people and their government.
"It is the biggest crisis since the revolution," he said.
About 400 pro-reform students, many wearing green face masks to conceal their identity, gathered earlier at a mosque in Tehran University and demanded Ahmadinejad's resignation.
Some said religious militia had attacked their dormitory. "They hit our friends and took away at least 100 students. We have no news about their whereabouts," said another student.
University officials denied the reported incidents.
A burnt-out shell of a bus or truck lay inside the university's dormitory compound, Reuters television pictures showed. Across the road, a bank office had been gutted by fire.
Outside the British embassy, Ahmadinejad supporters chanted slogans against the "plots of Iran's Western enemies."
Israeli Defence Minister Ehud Barak again said his country reserved all options on Iran -- code for a possible attack on nuclear sites, which Tehran says are only for peaceful purposes.
"The triumph of extremism is bad news, as any victory of extremists should be defined," added Barak, whose country is believed to have the Middle East's only nuclear arsenal.
(Editing by Alistair Lyon and Janet Lawrence)
