Iran's opposition leaders will attend the nationwide "Qods Day" rally on Friday, a reformist website reported on Wednesday, a move that could lead to fresh anti-government protests.
The June presidential election, which was followed by huge opposition protests, plunged Iran into political turmoil and exposed deepening divisions within its ruling elite.
Opposition leaders say the poll was rigged to secure President Mahmoud Ahmadinejad's re-election. The authorities deny it.
Iranian authorities, including supreme leader Ayatollah Ali Khamenei, have warned the opposition against turning the annual anti-Israel rally into street protests against the clerical establishment.
Defeated presidential candidates Mirhossein Mousavi and Mehdi Karoubi said they would attend the anti-Israel rally. "Mousavi, Karoubi and former president Mohammad Khatami will participate in Friday's rally," said the reformist website, Mowjcamp.
Defying the authorities, some moderate websites have called for new anti-government protests on "Qods Day".
Witnesses said security forces had tightened control in streets leading to the prayer venue in central Tehran.
'Nothing to do with current government'
The late founder of Iran's 1979 Islamic revolution, Grand Ayatollah Ruhollah Khomeini, declared the last Friday of the Muslim fasting month of Ramadan as the "Qods (Jerusalem) Day" and called for nationwide rallies against Israel and in support of Palestinians.
State television said moderate cleric Akbar Hashemi Rafsanjani, who backed the opposition during the post-election unrest, had been replaced with a hardline cleric to lead the prayer sermon at Tehran University on Friday.
For the past 25 years, Rafsanjani, also head of a powerful arbitrary body, has led the sermon.
State media said Ahmadinejad would also address worshippers, a move which could provoke supporters of his election rivals to stage protests against the establishment.
Moussavi's kaleme.com website said "Qods Day" was initiated by Khomeini and had nothing to do with the current government, calling on his supporters to join the rally.
Rights groups say thousands of people, including senior pro-reform figures, were arrested after the election, though most have been freed. The opposition says more than 70 people died during street protests after the vote. It contradicts the official death toll of 36 people.
Hardliners have portrayed the opposition protests as a foreign-backed bid to undermine the Islamic government system.