* Opposition figure says disputed vote is "turning point"
* Fears worsening "political suppression"
TEHRAN, June 15 (Reuters) - An opposition politician said on Monday that Iran's disputed presidential election had exposed deepening divisions in the establishment and the Islamic Republic faced its biggest crisis since the 1979 revolution.
Ebrahim Yazdi, leader of the banned Freedom Movement, also said seven of its members had been detained after last Friday's vote and warned of worsening "political suppression" in Iran.
"It is a turning point in the history of the Islamic Republic," he told Reuters in an interview in his Tehran home.
Yazdi was foreign minister in Iran's first government after the revolution that overthrew the U.S.-backed shah three decades ago, but was sidelined as religious hardliners took control.
He was speaking two days after the Interior Ministry declared that hardline President Mahmoud Ahmadinejad had won a landslide victory against pro-reform candidate Mirhossein Mousavi, sparking violent protests in Tehran and elsewhere.
Mousavi, a former prime minister, denounced the election outcome as a "dangerous charade" and has formally called for it be annulled, citing vote-rigging and other irregularities.
Interior Ministry officials have rejected accusations of election fraud and Supreme Leader Ayatollah Ali Khamenei, Iran's top authority, has called on Iranians to back their president.
The election campaign was marked by unprecedented mudslinging, with Ahmadinejad accusing an influential cleric backing Mousavi of corruption in a televised debate. His rivals said he lied about the state of the economy.
Yazdi said Ahmadinejad's attacks on his opponents have opened a "Pandora's box" which had led to a deep crisis within the Islamic state's establishment.
"The result of such a crisis now is that the rift among the ... personalities in the revolution is getting deeper and deeper," Yazdi said.
"It is also between people and their government ... a rift between state and the nation," he said. "It is the biggest crisis since the revolution."
Tens of thousands of people marched in central Tehran on Monday, defying an Interior Ministry ban, to express support for Mousavi.
Yazdi is an important opposition voice in Iran but has no influence on state policy and has limited popular support.
On Monday, a leading reformer said police had detained over 100 reformers, including a brother of former President Mohammad Khatami. Police denied Khatami's brother had been arrested.
Yazdi said seven Freedom Movement members had also been detained over the last two days.
"The number of detainees is increasing ... I'm afraid that there will be more severe political suppression," he said.
Human rights groups and Western diplomats say Iran has stepped up a crackdown on dissenting voices since Ahmadinejad came to power in 2005, targeting student activists, labour figures and women's rights campaigners.
Analysts say this may have been in response to Western pressure over Iran's nuclear programme, which the United States suspects is aimed at making bombs, a charge Tehran denies.
Iran also rejects accusations of human rights abuse. Ahmadinejad on Sunday said Iranians enjoyed "absolute freedom."
Yazdi called the way the election process had been conducted "very suspicious" and said his party wanted all ballots to be counted again in the presence of representatives of the four candidates.
"This would be a very important legal step if they wanted to authenticate the result of the election," he said. (Editing by Richard Balmforth)
Our Standards: The Thomson Reuters Trust Principles.