YANGON, Myanmar (AP) — Security forces fired warning shots and tear gas canisters while beating Buddhist monks and hauling others away in trucks today as authorities tried to stop anti-government demonstrations, the first mass arrests since protests erupted last month.

About 300 monks and activists were arrested across Yangon, according to an exile dissident group, and reporters saw a number of monks — who are highly revered in Myanmar — being dragged into trucks.

A Norway-based dissident radio station, the Democratic Voice of Burma, said that one monk was killed and several injured in clashes in downtown Yangon. The death could not be confirmed by other sources.

“There have been lots of clashes in different places between the demonstrators and the riot police and the troops. The troops opened fire into the crowd, and they also used tear gas and some Buddhist monks have been beaten up,” said Aye Chan Naing, the station’s editor, citing reports from his reporters in Yangon, who were trying to confirm reports of three other monks killed.

The junta had banned all public gatherings of more than five people and imposed a nighttime curfew following eight days of anti-government marches led by monks in Yangon and other areas of the country, including the biggest protests in nearly two decades.

A march toward the center of Yangon followed the tense confrontation at the city’s famed Shwedagon Pagoda between the protesters and riot police.

“It’s scary here. They will kill us, monks and nuns. Maybe we should go back to normal life as before,” said a teenage nun, her back pressed against the back of a building near the scenes of chaos.

But a student at a roadside watching the arrival of the demonstrators said, “If they are brave, we must be brave. They risk their lives for us.”

Both spoke on condition of anonymity because of fear of reprisals.

The latest developments could further alienate already isolated Myanmar from the international community and put pressure on China, Myanmar’s top economic and diplomatic supporter, which is keen to burnish its international image before next year’s Olympics in Beijing.

But if the junta backs down, it risks appearing weak and emboldening protesters, which could escalate the tension.

When faced with a similar crisis in 1988, the government harshly put down a student-led democracy uprising. Security forces fired into crowds of peaceful demonstrators and killed thousands, traumatizing the nation.

The potential for a violent crackdown already had aroused international concern, with pleas for the junta to deal peacefully with the situation coming from government and religious leaders worldwide. They included the Dalai Lama and South Africa’s Archbishop Desmond Tutu, both Nobel Peace Prize laureates like detained Myanmar opposition leader Aung San Suu Kyi.

British Prime Minister Gordon Brown today called for an urgent U.N. Security Council meeting on Myanmar, or Burma, and urged the military regime there to be restrained in reacting to protests.

“The whole world is now watching Burma and its illegitimate and repressive regime should know that the whole world is going to hold it to account,” Brown added.

“The age of impunity in neglecting and overriding human rights is over.”

About 5,000 monks and 5,000 students along with members of detained opposition leader Aung San Suu Kyi’s pro-democracy party set off from Shwedagon to the Sule Pagoda in the heart of Yangon, but were blocked by military trucks along the route.

Other blocs of marchers fanned out into streets in the downtown area with armed security forces attempting to disperse them. There were reports of destruction of property but it was unclear whether this was carried out by the demonstrators or pro-junta thugs, who were seen among the troops and police.

About 100 monks stayed behind at the eastern gate of the Shwedagon, refusing to obey orders to disperse after riot police there failed to dislodge them with tear gas, batons and warning shots.

Witnesses said an angry mob at the pagoda burned two police motorcycles.

A branch of Suu Kyi’s National League for Democracy exiled in Thailand said 300 people had been arrested in Yangon, most of them in a western suburb of the city. The number could not be independently confirmed.

Soldiers with assault rifles had earlier blocked all four major entrances to the soaring pagoda, one of the most sacred in Myanmar, and sealed other flash points of anti-government protests.

In Myanmar’s second largest city of Mandalay, more than 100 soldiers armed with assault rifles deployed around the Mahamuni Paya Pagoda

“We are so afraid; the soldiers are ready to fire on civilians at any time,” a man near the pagoda said, speaking on condition of anonymity for fear of reprisals.

Authorities announced the ban on gatherings and a 9 p.m. to 5 a.m. curfew through loudspeakers on vehicles cruising the streets of Yangon and Mandalay Tuesday.

A comedian famed for his anti-government jibes became the first well-known activist rounded up after the curfew was imposed.

Zarganar, who uses only one name, was taken away from his home by authorities shortly after midnight, with family members saying authorities told them the 45-year-old had been “called in for temporary questioning.”

Zarganar, along with actor Kyaw Thu and poet Aung Way, led a committee that provided food and other necessities to the Buddhist monks who have spearheaded the protests. He earlier had been imprisoned twice and his comedy routines were banned for their satirical jokes about the regime.

The fates of the actor and poet were not immediately known.

President Bush on Tuesday announced new U.S. sanctions against Myanmar, formerly known as Burma, accusing the military dictatorship of imposing “a 19-year reign of fear” that denies basic freedoms of speech, assembly and worship.

“Americans are outraged by the situation in Burma,” Bush said in an address to the U.N. General Assembly in New York.

Bush said the U.S. would tighten economic sanctions on leaders of the regime and their financial backers, and impose an expanded visa ban on those responsible for human rights violations and their families.

The European Union also threatened to strengthen existing sanctions against the regime if it uses violence to put down the demonstrations.

The current protests began Aug. 19 after the government hiked fuel prices in one of Asia’s poorest countries. But they are based in deep-rooted dissatisfaction with the repressive military rule that has gripped the country since 1962.

The protests were faltering when the monks took the lead last week, assuming the role of a moral conscience they played in previous struggles against British colonialism and military dictators.

The head of the country’s official Buddhist organization, or Sangha, issued a directive Monday ordering monks to stick to learning and propagating the faith, saying young monks were being “compelled by a group of destructive elements within and without to break the law,” the state-run New Light of Myanmar newspaper said.