Iranian riot police are reported to have clashed with demonstrators defying government decrees to stop street protests over disputed elections.
Eyewitness reports say there have been clashes near the parliament building in the capital Tehran, in the streets around Baharestan Square.
Severe reporting restrictions in Iran mean the BBC cannot verify the reports.
The new protests came hours after Iran's supreme leader said he would "not yield" over the election result.
Ayatollah Ali Khamenei again said the result would stand, despite days of protests in which at least 17 people are reported to have died.
See map of central Tehran
The ayatollah has repeatedly demanded that the protests stop, but his calls have gone largely unheeded.
In another development, Venezuelan President Hugo Chavez said he believed the US was behind the protests in Iran.
He offered no evidence but said the unrest in Iran followed a pattern seen in various countries, where the CIA and "the imperial hand" of European countries were involved.
He spoke just hours after it was confirmed that the US and Venezuela were to return their ambassadors to each other's countries following tit-for-tat expulsions last year.
Correspondents say that while Mr Chavez has repeatedly said he respects US President Barack Obama, he is still committed to countering Washington's global influence.
'Batons and tear gas'
Witnesses told the Associated Press that police beat protesters with batons, fired tear gas and shot into the air to disperse the crowd on Wednesday.
12 June Presidential election saw incumbent Mahmoud Ahmadinejad re-elected with 63% of vote
Main challenger Mir Hossein Mousavi called for result to be annulled on grounds of electoral fraud
Street protests saw at least 17 people killed and foreign media restricted
Although some demonstrators fought police, others fled to another square about 2km (1.2 miles) to the north, the witnesses said.
Another witness told Reuters that the crowd had been dispersed by tear gas, but did not know of any casualties.
The main protest leader, former prime minister Mir Hossein Mousavi, has not been seen in public for days, but his website quoted his wife as saying the protests would continue.
Zahra Rahnavard was also quoted as demanding the release of people detained since the election. They include 25 employees of her husband's newspaper.
"It is my duty to continue legal protests to preserve Iranian rights," she was quoted as saying on the website.
Iranian riot police on motorbikes patrol a road near parliament in Tehran, 25 June
Motorcycle police could be seen near the parliament on Wednesday
President Mahmoud Ahmadinejad was declared the winner of the 12 June poll.
Mr Mousavi alleges the election was rigged and is demanding a re-run.
The ayatollah had earlier agreed to extend by five days the amount of time allowed to examine complaints of electoral fraud.
But Iran's state-run Press TV channel said on Wednesday that a partial recount of the vote had verified the result, although it did not give details.
Another defeated candidate, the moderate Mehdi Karoubi, has reportedly denounced the new government as "illegitimate", Reuters adds.
"I do not accept the result and therefore consider as illegitimate the new government," he is quoted as saying on his website.
"Because of the irregularities, the vote should be annulled."
Iran has accused foreign governments of inflaming the protests.
Tehran said on Wednesday it was considering downgrading ties with Britain, after expelling two diplomats the previous day for "activities incompatible with their status".
The UK later announced that two Iranian diplomats were being sent home in retaliation.
Washington said on Wednesday it had rescinded invitations to Iranian diplomats to attend US 4 July celebrations held by embassies around the world.
A White House spokesman said Iranians had not replied anyway.
The BBC's Kim Ghattas, in Washington, says it is the first concrete step taken by the Obama administration in protest at Tehran's crackdown on demonstrators.
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