YANGON — The military government banned assemblies of more than five people and imposed curfews in Burma’s two largest cities today, after thousands of Buddhist monks and sympathizers defied orders to stay out of politics and protested once again.

Truckloads of soldiers converged on Yangon after the monks, cheered on by supporters, marched out for an eighth day of peaceful protest from Yangon’s soaring Shwedagon Pagoda, while some 700 others staged a similar show of defiance in the country’s second largest city of Mandalay.

“The protest is not merely for the well being of people but also for monks struggling for democracy and for people to have an opportunity to determine their own future,” one monk said, speaking on condition of anonymity fearing reprisals from officials. “People do not tolerate the military government any longer.”

President Bush today announced new American sanctions against Burma accusing the military dictatorship of imposing “a 19-year reign of fear” that denies basic freedoms of speech, assembly and worship.

The 9 p.m. to 5 a.m. curfew and the meeting ban were announced late today through loudspeakers mounted on vehicles cruising through the streets of Yangon and Mandalay, witnesses said. The announcement said the measures would be in effect for 60 days.

The measures, after a week of relative inaction by the government, throws down a challenge to its opponents. Should the protesters defy the new regulation, the junta will have no choice but to use force or back down.

Using force, especially against monks, who are revered in predominantly Buddhist Burma, might intimidate some people, but could also stir anger against the regime at home and abroad. So far, the government had been handling the monks gingerly,

But backing down would also carry the risk of emboldening protesters even more.