Up to 10,000 Burmese Buddhist monks and civilians have defied police tear gas and live bullets on the ninth day of protests against the military rulers.
At least one monk was killed, hospital sources in the main city of Rangoon said. The government has confirmed one death, without giving details.
Witnesses described monks with blood on their shaved heads as police charged at the Shwedagon pagoda in Rangoon.
Meanwhile, the UN said it was sending a special adviser on Burma to the region.
The BBC's James Robbins says Ibrahim Gambari's mission - if he is allowed into Burma - will be to urge the regime to stop using force and to start moving towards full democracy.
Mr Gambari will first brief the UN Security Council at an emergency meeting on Wednesday evening.
Permanent members Russia and China have argued that the situation in Burma is a purely internal matter.
The confrontation in Burma has become a battle of wills between the country's two most powerful institutions, the military and the monkhood, and the outcome is still unclear, the BBC's South East Asia correspondent, Jonathan Head, says.
Analysts fear a repeat of the violence in 1988, when troops opened fire on unarmed protesters, killing thousands.
The scenes of turmoil witnessed during the day ended as a night-time curfew took hold.
A statement by Burma's military government on state radio said one person had been killed and three others injured - the first official confirmation that the violence had caused casualties.
Earlier, a hospital source in Rangoon told the BBC that the monks were beaten with rifle butts, and that taxi drivers had transported the injured to nearby medical facilities.
Unconfirmed reports spoke of several dead.
The British ambassador to Burma, Mark Canning, told the BBC that people had shown their determination to demonstrate, despite a number of them being severely beaten.
He said at one point there were almost 10,000 people outside the embassy.
"There was a nucleus of perhaps 1,000 monks with probably 8,000 or 9,000 civilians - many women, many students.
"They have marched in big columns throughout various areas of the city. They were entirely peaceful," he said.
Our correspondent says that for all their brutality, the security forces were clumsy. They failed to prevent demonstrators from making their way through the city and their attacks on the monks only inflamed public anger - none of which was reflected on state television.
A statement read out on air said the authorities were handling the situation "most softly to avoid incidents desired by destructive elements while protecting the people".
Large demonstrations also took place in the cities of Mandalay and Sitwei, but the security forces there reportedly did little to prevent them.
A clampdown on the media by Burma's military government - which has banned gatherings of five people or more in addition to imposing a curfew - has made following the exact course of the protests difficult.
It is known that on Wednesday thousands of monks and opposition activists moved away from Shwedagon pagoda, heading for Sule pagoda in the city centre.
Others headed for the home of detained opposition leader Aung San Suu Kyi.
Reports suggested they were prevented from reaching it but other demonstrators did gather at Sule to jeer soldiers.
Troops responded by firing tear gas and live rounds over the protesters' heads, sending people running for cover.
Monks marching to the home of Aung San Suu Kyi reportedly urged civilians not to join them and not to resort to violence.
But elsewhere witnesses said civilians were shielding the marching monks by forming a human chain around them.
One BBC News website reader said: "The junta are using dirty tactics - they don't fire guns but beat people with rifle butts. The monks defiantly did not fight back."
The protests were triggered by the government's decision to double the price of fuel last month, hitting people hard in the impoverished nation.
US President George W Bush has announced a tightening of US economic sanctions against Burma.
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