TEHRAN, (Reuters) – Baton-wielding riot police clashed with opposition backers in Tehran who used a Shi’ite religious festival to stage new anti-government demonstrations on Saturday, an opposition website and witnesses said.

The reformist Jaras website also said security forces fired tear gas and warning shots to disperse protesters and also attacked a building housing an Iranian news agency, ISNA, where it said some demonstrators had sought shelter during the unrest.

At least two people were injured as police chased after demonstrators into the downtown building, a witness said.

In a sign the protests were spreading, another Tehran resident later said supporters of opposition leader Mirhossein Mousavi, chanting “Death to the dictator”, clashed with police near a mosque in northern Tehran where reformist former president Mohammad Khatami had been due to speak.

“They are chasing people and beating them and trying to disperse them, but even ordinary Iranians are stopping their cars and shout ‘Ya Hossein, Mirhossein’,” he said. Jaras said police also fired tear gas also during that incident.

The reformist Parlemannews website said dozens of hardliners disrupted Khatami’s speech by attacking the venue, which is located in a compound where late revolutionary leader Ayatollah Ruhollah Khomeini used to live.

“A few minutes ago over 50 hardliners used chains, batons and pepper spray to attack a venue … where Khatami was giving a speech,” it said.

The outbreak of clashes during a two-day major Shi’ite Muslim religious mourning ritual underlines escalating tension in the Islamic Republic, six months after a disputed election plunged the major oil producer into turmoil.

It was not possible to independently verify the Jaras reports as foreign media are banned from covering protests.

The official IRNA news agency said the “rioters” in central Tehran numbered only 150, adding they wanted to disrupt the mourning ceremonies but that police dispersed them.

Despite scores of arrests and security crackdowns, opposition protests have repeatedly flared since the June poll, which the opposition says was rigged to secure hardline President Mahmoud Ahmadinejad’s re-election.Jaras said, “Well-equipped security forces are clashing violently with backers of the opposition in many parts of downtown Tehran” and added later “riot police are shooting into the air in Enqelab square to disperse demonstrators who chant anti-government slogans”.

IRNA accused foreign media of exaggerating the “unsuccessful gathering of rioters” and of trying to encourage people to take to the streets.

The authorities had warned the pro-reform opposition against staging any new rallies during Tasoua and Ashura on Dec. 26-27 when Shi’ite Muslims gather to mark the 7th century martyrdom of a grandson of the Prophet Mohammad, Imam Hossein.

This year’s Ashura on Sunday coincides with the traditional seventh day of mourning for leading dissident cleric Grand Ayatollah Hossein Ali Montazeri, who died a week ago at the age of 87 in the holy Shi’ite city of Qom.

A spiritual patron of the movement for opposition leader Mirhossein Mousavi, he was a fierce critic of the hardline clerical establishment.

Indicating possible further unrest when the religious commemoration culminates on Ashura, the opposition urged people to gather in the same Tehran area also on Sunday morning, according to mobile phone text messages.

Police chief Esmail Ahmadi-Moqadam said his force would firmly confront any unrest that caused “destruction and chaos” and arrest the leaders, ISNA reported.

Ahmadinejad’s re-election kindled the biggest unrest in the Islamic state’s 30-year history and split the political and clerical establishment.

Authorities deny the opposition’s vote rigging charges and have portrayed huge protests that erupted after the poll as a foreign-backed bid to topple the Islamic establishment, accusing leading reformers of fomenting post-election violence.

Thousands of people were arrested after the poll. Most of them have since been freed, but more than 80 have received jail sentences of up to 15 years in connection with protests and violence after the vote, the judiciary says.

Iran’s internal unrest has complicated a long-running international dispute over its nuclear programme, which the West believes may have military ends, not just civilian purposes.

Saturday’s reported clashes come just days before an end-of-year deadline set by world powers for Iran to agree a U.N.-drafted deal to ship most of its low-enriched uranium abroad in exchange for fuel for a Tehran research reactor.

Ahmadinejad said Iran’s foreign foes could not harm the Islamic state from inside the country, Fars News Agency said. “They don’t know that a nation which is ready to sacrifice its life for its religious figures will destroy all their satanic attempts,” he said. He also called European politicians “one more stupid than the other”, the semi-official news agency added.