BANGKOK, Thailand — Army troops Monday arrested the leader of monthlong demonstrations against Thailand's beleaguered government and repeatedly opened fire to disperse hundreds of his pro-democracy followers. But the tough action failed to quell two days of violence in Bangkok, and pitched street battles raged early today.

Prime Minister Suchinda Kraprayoon, who has been the target of protests since his appointment last month, went on national television and blamed the pro-democracy demonstrators for instigating violence "to achieve their political aims."

Suchinda said the government had "no other choice than to use military force" to halt the violence, and he promised to return the nation of 55 million people to peace as soon as possible.

Estimates by newspapers and news agencies placed the casualty toll in the violence, which started Sunday night, at more than 15 dead and 500 wounded. Some Thai newspapers said that more than 100 people were killed in heavy fighting Monday night. Several of the injured were reported to be foreigners.

The bloodiest fighting took place shortly before midnight outside the capital's Royal Hotel, where many demonstrators had taken refuge to avoid withering police and army fire.

Angry protesters commandeered city buses and tried to crash through police lines, and the troops cordoning off the area opened fire with machine guns on the buses, which were packed with young protesters.

The army then chased the demonstrators through the narrow streets, firing directly into the crowds in an effort to disperse them. The streets were littered with what appeared to be dead and seriously wounded people. The death toll appeared certain to rise sharply.

A makeshift hospital was set up in the lobby of the Royal Hotel, where doctors performed emergency operations until police arrived and arrested many of the Thais there. They were taken away in army trucks to an unknown destination.

The tough measures provoked an angry response from a growing crowd of demonstrators, who went on a rampage through nearby streets that contain many of the government's office complexes. Buildings housing the government Public Relations Department and another belonging to the Lottery Department were set on fire.

Dozens of cars, fire trucks and city buses were also set ablaze. Protesters drove gasoline-filled vehicles into barricades, causing huge, fiery explosions.