Thai authorities have declared a state of emergency across the capital, Bangkok, and the surrounding areas, in an attempt to stem recent protests.
The move comes one day after anti-government protesters forced the cancellation of a major Asian summit in the country.
In a television address, Thai Prime Minister Abhisit Vejjajiva said the state of emergency was necessary to restore order.
"I want to inform everyone that the state of emergency and all the regulations that go with it, I declare it is to bring the situation back to normal as soon as possible. I will ensure that the government will try to avoid any damage that might cause more violence," Abhisit said.
Meanwhile bands of "red-shirt" protestors roamed areas of Bangkok. Some reports say shots were fired near the Interior Ministry.
Earlier in the day, Abhisit vowed to take action against those who were involved in the April 11 incident at the beach resort of Pattaya, when protesters forced authorities to scrap a summit of the Association of Southeast Asian Nations (ASEAN) and evacuate foreign leaders.
"Whatever the protesters demand within the frame of democracy and justice, they can send their representatives to talk to me. But we will take serious legal action against every protester who motivates others or acts against the law -- with no exception," Abhisit said.
Also on April 12, a leader of the protests, Arisman Pongruengrong, was arrested after returning to his home in Bangkok.
Pre-summit street protests by supporters of the ousted Prime Minister Thaksin Shinawatra in the capital this week drew up to 100,000 people.
Supporters of Thaksin, who was deposed in a 2006 military coup and remains in self-imposed exile to avoid a two-year jail term for corruption, want Abhisit to step down and are calling for fresh elections.
Abhisit was elected in a parliamentary vote four months ago after the previous government was dissolved by a court decision for election fraud.
compiled from agency reports