TEHRAN (AFP) – Police used batons and teargas to break up an opposition protest in central Tehran on Wednesday, while huge crowds staged a noisy anti-US rally nearby to mark the storming of the American embassy by students 30 years ago.

US President Barack Obama, meanwhile, in a statement marking the anniversary of the event that sparked decades of hostility between America and Iran urged Tehran to make choices that would end its international isolation.

Witnesses said the violent clashes occurred at Haft-e-Tir square in the heart of the capital when riot police armed with batons and firing teargas moved in on a crowd of several hundred opposition supporters staging a protest.

The protesters, who were chanting “Death to the dictator,” refused to disperse and dozens were beaten or arrested. Groups of pro-government hardliners also gathered at the square chanting “Death to America.”

Opposition website Mowzcamp.com reported that opposition leader Mehdi Karroubi was among the protesters at the square but left quickly after he and his supporters came under attack by the hardliners.

The report could not immediately be confirmed.

Away from Haft-e-Tir square, opposition supporters — numbering several thousand in all — gathered in small groups on many street corners and side roads, witnesses said.

Staging brief demonstrations during which they chanted “Death to the dictator,” and “Ya Hossein, Mir Hossein” — in praise of main opposition leader Mir Hossein Moussavi — the mainly-young protesters quickly moved on to new sites when police tried to disperse them.

Witnesses said the entire city centre had become a stage for “cat and mouse games” between police on bikes and youthful protesters.

According to the Irna news agency, protesters set fire to rubbish bins and attacked a bus, smashing its windows. It said two policemen were injured in the clashes and hospitalised.

Opposition supporters have since June been staging protests at every opportunity in Tehran against the re-election of Mahmoud Ahmadinejad in a presidential vote they claim was massively rigged.

About a kilometre (mile) away, outside the former US embassy complex — dubbed the “Den of Spies” — thousands of Iranians gathered from early morning chanting slogans such as “Death to America” and “Death to Israel,” witnesses said.

They also smashed up posters they had brought with them of the American “Uncle Sam” symbol and chanted “The blood in our veins is a gift to our leader” — a reference to Iranian supreme leader Ayatollah Ali Khamenei.

The crowd was constantly swelled by people arriving on foot and by bus, witnesses said.

Wednesday’s anniversary, which has turned into a cornerstone of the Islamic regime, marks the capture by radical Islamist students of the US embassy compound on November 4, 1979 — just months after the Islamic revolution toppled the US-backed shah.

The students, who took 52 American diplomats hostage and held them for 444 days, said they were responding to Washington’s refusal to hand over the deposed shah, Mohammad Reza Pahlavi.

The two countries broke diplomatic ties after the event, which have yet to be restored.

Obama in his statement urged Iran to look to the future rather than the past.

“We have heard for 30 years what the Iranian government is against; the question, now, is what kind of future it is for,” he said.

“It is time for the Iranian government to decide whether it wants to focus on the past, or whether it will make the choices that will open the door to greater opportunity, prosperity and justice for its people.”

US-Iranian relations deteriorated even further during the tenure of former US president George W. Bush, who lumped Iran into an “axis of evil” along with North Korea and Saddam Hussein’s Iraq.

During his first term as president, Ahmadinejad stepped up Tehran’s anti-US tirade.

And although Washington has made diplomatic overtures towards Tehran under Bush successor Barack Obama, Khamenei said Iran still distrusts the United States.

“Every time they have a smile on their face, they are hiding a dagger behind their back,” he said on Tuesday.

The anniversary comes at a time when Washington is backing a sensitive nuclear fuel deal for Tehran brokered by the UN atomic watchdog.