Burma's military junta has isolated Aung San Suu Kyi, the opposition leader, and closed the offices of her National League for Democracy (NLD), after four people died in rioting at a political rally.
Ms Suu Kyi was expected to be brought to the capital, Rangoon, late last night, although the government denied she was under formal arrest.
The 1991 Nobel peace laureate, Burma's most prominent political voice, was taken into what Rangoon authorities described as "protective custody" after a two-hour riot at a stop on her tour of northern Burma on Friday night. Whether Ms Suu Kyi had agreed to be detained is unclear, as she is held incommunicado. Nineteen other NLD party leaders were also reported to be in custody.
Officials said that four people had been killed and 50 injured when members of the government-sponsored Union Solidarity Development Association clashed with more than 5,000 opposition supporters in Yaway Oo, about 400 miles north of the capital.
"They are local militias, equipped with slingshots and bamboo sticks, who come out and harass NLD supporters," said Aung Zaw, the exiled editor of The Irrawaddy, published in Bangkok. Violence was triggered when Ms Suu Kyi's motorcade was cut off, witnesses said.
It is feared that the renewed crackdown will rule out any meaningful political discussions between Ms Suu Kyi, who was elected president of Burma in 1990, and the military regime that has prevented her from taking office and held her prisoner on and off for nearly eight years.
In May last year, after Ms Suu Kyi was freed from 19 months of house arrest, political suppression by the military appeared to be easing. But Ms Suu Kyi's popularity has not waned, as the junta had hoped, and her recent rallies were well attended. The authorities decided to act before Ms Suu Kyi was due to address a huge gathering in Mandalay.
Diplomats fear the bloodshed may derail United Nations efforts to facilitate a democratic future for Burma, a country under military dictatorship for four decades and renamed Myanmar in 1989.
Kofi Annan, the UN secretary general, said on Saturday that the events "underline the urgent need for national reconciliation in Myanmar".
Red Cross representatives in Rangoon are reported to be seeking access to Ms Suu Kyi, whose "inflammatory speeches" have upset the generals.
On the 13th anniversary of her election last Tuesday, Ms Suu Kyi called for the regime to recognise her victory and release its stranglehold on the Burmese people. For the past month, she has derided the military's lack of progress on reform and its reluctance to negotiate with her.
Government forces were said to be surrounding the homes of her political allies in Rangoon after raiding party offices. Ten NLD party loyalists were arrested last month and more than 1,300 are held as political prisoners. Razali Ismail, a United Nations special envoy, is scheduled to arrive in Rangoon to attempt to restart talks on Friday.Reuse content