TEHRAN, Iran _ Iran's President Mahmoud Ahmadinejad lashed out at Israel and the West saying Friday the Holocaust was a lie and a pretext for occupying Palestinian lands, while hard-liners attacked a reformist cleric who was marching with the opposition at an anti-government rally in Tehran.

Thousands of opposition supporters held protests in competition with government-sponsored mass rallies to mark an annual anti-Israel commemoration, the Quds Day that reflects the Persian nation's sympathy with the Palestinians.

Tens of thousands joined the government-organized marches in downtown Tehran for the occasion, while baton-totting police and security troops, along with the pro-government Basij militia that helped crush mass street protests this summer against Ahmadinejad's re-election, fanned out along main squares and boulevards.

At one of the opposition rallies, a group of hard-liners came up and attacked reformist former president, Mohammad Khatami, pushing him to the ground, according to a reformist Web site. The report cited witnesses as saying the opposition activists rescued Khatami and quickly repelled the assailants.

Khatami has sided with the opposition in the post-election crisis that has gripped Iran since Ahmadinejad's June 12 re-election. Another reformist Webs site said Khatami's turban was disheveled and he was forced to leave the march.

Witnesses said a group of hard-line demonstrators tried to attack opposition leader Mir Hosein Mousavi as he joined another of the opposition marches in downtown Tehran. The reports could not independently verified because Iranian authorities have banned foreign media from covering opposition rallies. There were no further details and reports said Mousavi quickly left the streets afterward.

Customarily on Quds Day, Tehran residents gather for pro-Palestinian rallies in various parts of the city, marching through the streets and later converging for the prayers ceremony. The ceremony was established in 1979 by the leader of the Islamic Revolution and founder of present-day Iran, Ayatollah Ruhollah Khomeini.

Since midmorning, opposition supporters poured out on the streets in green T-shirts and wearing green wristbands _ a color symbolizing the opposition movement _ and marched with fingers raised in the V-sign for victory, chanting "Death to the Dictator."

Others shouted for the government to resign, carried small photos of Mousavi, while some women marched with their children in tow.

There were also chants of: "Neither Gaza nor Lebanon, but our life is for Iran" _ a slogan defying the regime's support for Palestinian militants in Gaza and Lebanon's Hezbollah guerrilla.

Just hundreds of yards (meters) away on the main Keshavarz Boulevard, thousands of Ahmadinejad supporters marched carrying huge photographs of the president and also the country's Supreme Leader Ayatollah Ali Khamenei. Some in the government-sponsored rally chanted: "Death to those who oppose the Supreme Leader!"

At the climax of the occasion, Ahmadinejad addressed worshippers before Friday prayers at the Tehran University campus, reiterating his anti-Holocaust rhetoric that has drawn international condemnation since 2005, questioning whether the "Holocaust was a real event" and saying Israel was created on "false and mythical claims."

He also accused Israel of inciting foreign-based Iranian opposition groups to stage protest rallies against his re-election. Ahmadinejad claimed Zionists plan to stage protests during his visit next week to New York to attend the U.N. General Assembly.

"Rest assured, Iranian people will not appreciate such a move," said Ahmadinejad.

Ahmadinejad also accused world powers of double standards in favor of Israel and of disregarding violations of Palestinian rights. He repeated his old predictions that Israel would soon cease to exist and urged people to stand up against Israel's "Zionist regime as a national and moral duty."

Even though the sheer numbers of the government-sponsored marches overshadowed the opposition rallies, Friday saw the largest opposition demonstration since mid-July, when authorities cracked down heavily on the protesters.

Rumors of small-scale clashes elsewhere could not be immediately confirmed, while witnesses said another opposition leader, Mahdi Karrubi, appeared at one of the opposition marches. There have been concerns the regime would act to detain the opposition leaders if they joined anti-governmet street protests.

The semi-official Fars news agency reported that Akbar Hashemi Rafsanjani, another ex-president and supporter of Mousavi, participated in one of the opposition marches Friday.

Rafsanjani had led Friday prayers on Quds Day for the past 25 years, but was this week banned from the service and replaced with a hard-line cleric and supporter to Ahmadinejad, Ahmad Khatami.

Iran's elite Revolutionary Guard warned the opposition on Thursday against holding anti-government demonstrations, saying that if they attempted "any sort of violation and disorder" they will encounter "strong confrontation."

Khamenei, who has final say on all state matters, also warned last week against the opposition using Quds Day for other purpose than demonstrating solidarity with the Palestinians.

The pro-reform camp claims Mousavi was the rightful winner of the presidential election and that the government faked the balloting in Ahmadinejad's favor. For a month after the June balloting, thousands of opposition supporters held street demonstrations against the alleged vote fraud but were met with a heavy government crackdown.

The opposition says at least 72 protesters were killed in the violence that followed the election, while government officials maintain that only 36 died in the unrest _ the worst in Iran since the 1979 Islamic Revolution that brought the current regime to power. Thousands were arrested, and the regime's opponents have charged some detainees were tortured to death in prison.