TEHRAN – Iranian police broke up a protest in Tehran and the hardline Revolutionary Guards said they would help crush what they called rioters opposing the re-election of President Mahmoud Ahmadinejad.

EDITORS' NOTE: Reuters and other foreign media are subject to Iranian restrictions on their ability to report, film or take pictures in Tehran.

In New York, U.N. Secretary-General Ban Ki-moon urged an immediate stop on Monday to use of force against civilians in the Islamic Republic and said Iranian authorities should respect civil rights in dealing with protests.

People in Tehran, in a gesture of defiance first used in the 1979 Islamic revolution and now adopted by pro-reform protesters, again chanted Allahu Akbar (God is greatest) from their rooftops at nightfall on Monday.

Witnesses said supporters of opposition leader Mirhossein Mousavi, officially beaten into second place by Ahmadinejad in the June 12 presidential election which he says was rigged, had earlier gathered in Tehran's Haft-e Tir square.

Iran's state Press TV channel said they were dispersed.

Residents said riot police, some on motorbikes, and members of the religious Basij militia were out in force.

One witness said that from his balcony he had seen a group of protesters chanting slogans being attacked by the Basij, who dragged the demonstrators out of a nearby house to which they had fled.

The Basiji were really aggressive and swearing at me to go inside, said the witness, who declined to be identified. I was scared they were going to break into my house too.

The statement on Monday by the Revolutionary Guards, viewed as the most loyal guardians of the ruling clerical establishment, clearly signaled a crackdown on any new unrest in the world's fifth-largest oil exporter.

In the current sensitive situation ... the Guards will firmly confront in a revolutionary way rioters and those who violate the law, said a statement on the Guards' website.

Mousavi called on Sunday for new protests by his supporters.

Ali Shahrokhi, head of parliament's judiciary committee, said Mousavi should be prosecuted for illegal protests and issuing provocative statements, the semi-official Fars news agency reported.

U.N. REACTION

A U.N. statement issued by Ban's press office said he was dismayed by the post-election violence, particularly the use of force against civilians.

It said Ban urged the authorities to respect fundamental civil and political rights, especially the freedom of expression, freedom of assembly and freedom of information.

Ban called on the Iranian government and the opposition to resolve their differences peacefully through dialogue and legal means, said the statement.

Iranian authorities have accused Western powers of supporting the protests -- the most widespread since the 1979 Islamic revolution -- and have not ruled out expulsions of some European ambassadors.

Sweden, the European Union's next president, said the bloc's members should consider drafting a plan to take in and provide aid to demonstrators at their embassies in Iran. Italy said it was prepared to open its embassy to wounded protesters.

Iranian state television said 10 people were killed and more than 100 wounded in demonstrations in Tehran on Saturday, which defied a warning from Supreme Leader Ayatollah Ali Khamenei.

The office of Tehran's prosecutor general blamed the weekend deaths on unknown vandals who had opened fire on civilians and killed people on Saturday, said Press TV.

Iranians on social networking sites called for mourning for Neda, a young woman shot dead on Saturday. Footage of her death has been watched by thousands on the Internet and her image has become an icon of the protests.

Witnesses said security officials prevented her funeral from going ahead, blocking roads leading to a central Tehran mosque where the ceremony was to have taken place.

Police were spraying paint on the cars of those who insisted on driving toward the mosque, said one witness.

Her fiance Caspian Makan told BBC Persian TV that Neda Agha-Soltan had been caught up accidentally in the protests.

She was near the area, a few streets away, from where the main protests were taking place, near the Amir Abad area. She was with her music teacher, sitting in a car and stuck in traffic, it quoted him as saying.

She was feeling very tired and very hot. She got out of the car for just a few minutes.

(Editing by Ralph Gowling)