Iranian riot police on motorcycles beat supporters of presidential challenger Mirhossein Mousavi who were protesting on Saturday against President Mahmoud Ahmadinejad's disputed election win.
The Al-Arabiya network reported at least three people dead in the riots, adding that Iranian security forces surrounded a neighborhood in which many reformists reside, including former President Hashemi Rafsanjani.
A Reuters reporter said she and others were beaten by police with batons, as the security forces chased and arrested some of the demonstrators staging a sit-in at Tehran's Vanak Square, one of the capital's busiest intersections.
At least three people were injured in the clash, which broke out after the Interior Ministry announced the hardline incumbent's resounding victory in Friday's vote.
Celebrating in Tehran (Photo: AFP)
Mousavi, a moderate, said in a statement he "strongly protested" against what he called many violations in the election. Interior Ministry officials rejected such allegations.
He said in a separate statement that members of his election headquarters had been beaten "with batons, wooden sticks and electrical rods." He did not give details.
Mousavi rejected the election results as rigged and urged his supporters to resist a government of "lies and dictatorship."
"I'm warning that I won't surrender to this manipulation," said a statement on Mousavi's Web site. "The outcome of what we've seen from the performance of officials ... Is nothing but shaking the pillars of the Islamic Republic of Iran's sacred system and governance of lies and dictatorship," it added.
Mousavi warned "people won't respect those who take power through fraud."
The headline on one of his Web sites read: "I won't give in to this dangerous manipulation."
The BBC television showed footage of policemen attacking protesters.
Up to 2,000 Mousavi supporters took part in the sit-in in the middle of the road, chanting: "Mousavi take back our vote! What happened to our vote?"
Protestors in Tehran (Photo: Reuters)
Hundreds of his backers later gathered in side streets near Vanak, chanting anti-Ahmadinejad slogans and bringing traffic to a standstill. "We are Iranians too," And "Mousavi is our president," they shouted.
The protests were a first reaction by Mousavi supporters, who thronged the streets of Tehran nightly in the run-up to Friday's vote, to Ahmadinejad's victory.
"I have never voted before. I did vote on Friday but it did not count," one middle-aged woman said near Vanak.
Some demonstrators later set rubbish bins on fire and taunted riot police. Some also threw stones at them. Police at times charged at the protesters who then fled, only to return shortly afterwards.
"The election was corrupt. If Ahmadinejad had won where are his supporters? How come they are not celebrating? said Reza, 25. "Most people think Mousavi won the election," said another young man, Saman.
Riots in Tehran (Photo: AP)
Elsewhere in Tehran, tires were set ablaze, witnesses said.
Scuffles broke out also early on Saturday between police and chanting Mousavi supporters in another Tehran square.
Police say they have increased security across the capital to prevent trouble.
Iran's Supreme Leader Ayatollah Ali Khamenei urged defeated presidential election candidates on Saturday to avoid provocations and to support the victor, Ahmadinejad.
Meanwhile, in Israel, ministers appeared unsurprised by Ahmadinejad's win, but emphasized that it should serve as an alert to the international community.
The international community must step up efforts to deal with Iranian terror and nuclear aspirations "immediately," given the results in Iran, Deputy Foreign Minister Daniel Ayalon said Saturday.
"In Israel, we had no illusions, because we knew there was no essential difference between candidates on the topics of terror and nuclear development. If there had been even a spark of hope for a change in Iran, the reelection of Ahmadinejad demonstrated once more the increasing threat from Iran," he said.
The results of Iranian presidential elections "are exploding in the face of those who thought that Iran was built for true dialogue with the free world, including a cessation of its nuclear program," added Regional Cooperation Minister Silvan Shalom.
"The election of Ahmadinejad sends a clear message to the world, that the current policy has won widespread support and thus, will continue. The United States and the free world must reassess their policy towards Iran regarding its nuclear program," he said.
Venezuelan President Hugo Chavez, on the other hand, immediately called to congratulate Ahmadinejad. According to the Iranian president's website, Chavez called his victory "a win for free nations" of the world.
Dudi Cohen, AP, Reuters, AFP contributed to the report