Tens of thousands of Iranian government supporters and dozens of opposition activists poured out Friday onto the streets of Tehran for coinciding marches marking an annual pro-Palestinian commemoration.

Iran security forces clashed with supporters of opposition leader Mir Hossein Mousavi and arrested at least 10 of them during the rallies, Reuters reported a witness as saying.

"Security forces just arrested over 10 people," the witness said." They are pushing protesters and beating them."

At least two protesters were reported injured.

A group of Iranian hard-liners also attacked a reformist former president while he was marching with opposition supporters.

A reformist Web site cites witnesses as saying the attackers pushed ex-President Mohammad Khatami to the ground. It says opposition activists rescued him and quickly repelled the assailants.

Khatami has sided with the opposition in the post-election crisis that has gripped Iran. Another reformist Webs site says his turban was disheveled and he was forced to leave the march.

Opposition supporters gathered despite warnings by the clerical establishment against anti-government rallies. There has not been a mass opposition demonstration since mid-July, when authorities cracked down heavily on the opposition.

Baton-totting police and security troops, along with the pro-government Basij militia that helped crush mass street protests this summer against Mahmoud Ahmadinejad's re-election, were deployed along main squares and boulevards.

Ahmadinejad joined one of the government-sponsored marches heading to the Tehran University campus where he was to address supporters before a Friday prayers service.

Both opposition leaders — Mousavi and Mahdi Karrubi — were to appear at the opposition rally, raising concerns for a showdown between security troops and opposition activists.

By midmorning in central Tehran, dozens of opposition supporters in green T-shirts and wearing green wristbands — a color symbolizing the opposition movement — marched with fingers raised in the V-sign for victory and 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 yard 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!"

The demonstrations mark Quds Day — an annual event dedicated to condemning Israel and expressing support for the Palestinians. Quds is Arabic for Jerusalem.

On Thursday, Iran's elite Revolutionary Guard warned opposition protesters 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, last week also warned the oppositions against using Quds Day for other purpose than demonstrating solidarity with the Palestinians.

The pro-reform camp claims Mousavi was the rightful winner of the June 12 presidential election and that the government faked the balloting in Ahmadinejad's favor. Since the vote, 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.

Customarily on Quds Day, Tehran residents gather for pro-Palestinian rallies in various parts of the city, march through the streets and later converge 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.

The Associated Press contributed to this report.