Supporters and opponents of Iranian President Mahmoud Ahmadinejad clashed in a Tehran square on Saturday evening and some cars were set on fire, a witness said, in a sign of rising tension ahead of the June 12 election.
The incident took place as rival supporters followed a televised debate between Ahmadinejad and pro-reform challenger Mehdi Karoubi on big screens at Sarv square in northwestern Tehran, the witness told Reuters.
It was the second night of sporadic unrest in the capital, after thousands of supporters of Ahmadinejad and another of his moderate challengers in the presidential election scuffled elsewhere in the capital on Friday evening.
Mainly young supporters of the election hopefuls have poured into the streets of Tehran during evenings as the election approaches, shouting, honking car horns and waving pictures of their candidates. At times, traffic has ground to a standstill.
With more than 60 per cent of Iranians under the age of 30, their votes will be crucial.
Ahmadinejad is being challenged by Karoubi, former Prime Minister Mirhossein Mousavi, and the conservative former head of Iran's elite Revolutionary Guards, Mohsen Rezaie.
Mousavi, a moderate who is hoping to win votes from both reformers and conservatives, is seen as Ahmadinejad's main opponent in the election.
In a heated debate, Ahmadinejad and Karoubi traded allegations on issues ranging from the economy of the world's fifth-largest oil exporter to Iran's foreign relations.
Ahmadinejad hit back at critics accusing him of stoking inflation with profligate spending of petrodollars since he came to office in 2005, saying the rate was declining and would soon fall below 10 per cent, compared with 18 per cent in March.
The rate, which peaked at nearly 30 per cent in October, was about 11 per cent when Ahmadinejad came to power four years ago pledging to share out Iran's oil wealth more fairly and reviving the values of its 1979 Islamic revolution.
Ahmadinejad also said economic growth and unemployment statistics compared favorable with those of previous governments. He challenged his opponents to make public their income and wealth, saying he had nothing to hide.
Karoubi, who is trying to expand his power base among reform-minded Iranians with a promise to dole out Iran's oil wealth, questioned the figures presented by Ahmadinejad.
"People are aware of the realities ... when they purchase meat they will feel inflation," said Karoubi, a cleric and former parliamentary speaker.
Rising consumer prices and lack of jobs are the loudest complaints among many Iranians, especially in big cities.
Ahmadinejad's critics say his fiery anti-Western speeches and questioning of the Holocaust have isolated Iran, which is at odds with the West over its disputed nuclear program.
Iran says it is for electricity generation, but a number of Western countries believe the aim is to build nuclear weapons.
In his debate with Ahmadinejad on Wednesday, Mousavi accused him of humiliating the Iranian nation by adopting an "extremist" foreign policy. Ahmadinejad accuses his rivals of trying to weaken the Islamic state by advocating detente with the West.