* EU increases pressure on Iran over election result
* France, Germany lead calls for investigation
* U.S. more cautious because of recent overtures - analyst
By Mark John
LUXEMBOURG, June 15 (Reuters) - The European Union increased pressure on Iran on Monday to agree to opposition demands to investigate President Mahmoud 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 result despite no sign of new pressure from the United States, their partner at talks intended to ensure Tehran does not develop nuclear weapons.
Defeated moderate candidate Mirhossein Mousavi has called for an investigation and wants the result of Friday’s election annulled. Tens of thousands of his supporters gathered in Tehran on Monday after earlier protests over the outcome.
Iran’s 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.
"The German government believes the allegations of manipulation of the vote must be examined quickly by the responsible bodies to remove the doubts about this result," government spokesman Thomas Steg told reporters in Berlin.
"We are greatly concerned about what we see as an over-reaction by the security forces in cracking down on protesters, people who have the right to express their opinions."
Ahmadinejad and Interior Ministry officials have dismissed allegations the vote was rigged. The president has called the election "free and healthy".
But the outcome has alarmed Western powers trying to persuade the world’s fifth-biggest oil exporter to curb nuclear work they suspect is intended to develop atomic weapons, a charge Iran denies.
"I asked today that the investigations demanded by the opposition be carried out," French Foreign Minister Bernard Kouchner told reporters after talks with other EU foreign ministers in Luxembourg.
The ministers were expected to issue a joint appeal later on Monday for an investigation and express concern about the use of force against demonstrators.
"There are signs of irregularities," German Chancellor Angela Merkel told a news conference in Berlin.
IMPACT ON NUCLEAR TALKS
British Foreign Secretary David Miliband made clear doubts about the fairness of the election could have an impact on talks on Iran’s nuclear programme which involve France, Britain, Germany, the United States, Russia and China.
"Our serious concern is about the implications of recent events for the engagement the international community seeks with the government of Iran," Miliband said.
He regretted Iran had not responded to efforts by U.S. President Barack Obama to break the deadlock over its nuclear programme, which include looking for ways for Washington to deal directly with Iran.
The United States has said it will not comment until it has been able to review the "whole process" and the authorities’ reaction, although Vice-President Joe Biden has cast doubt on the outcome and said Tehran may be suppressing free speech.
"When it comes to Iran the United States have recently stuck their necks out and are being overly cautious," said Daniel Rackowski of the Transatlantic Institute in Brussels.
"The United States probably know they will have to work with Ahmadinejad and they will be the ones doing the bulk of the negotiations, not the European Union. So I think the European Union can be more critical whereas (U.S. Secretary of State Hillary) Clinton will actually have to work with them."
EU foreign policy chief Javier Solana, who has acted as mediator in the major powers’ talks with Iran, said there had been few expectations of any major change in Iranian nuclear policy before the election, but the EU was still prepared to discuss the issue with Tehran.
"I hope very much that they will get engaged," he said. "I hope very much that at the end of the day the will of the people will be respected." (Additional reporting by Julien Toyer, Sarah Marsh and Timothy Heritage; writing by Timothy Heritage; Editing by Janet Lawrence)