Thai troops deployed amid Bangkok protests
Troops have been deployed in the Thai capital Bangkok to support riot police shielding official buildings from some 30,000 anti-government protesters.
Tear gas and water cannon were fired as protesters tried to breach barricades outside Government House.
Sunday is the eighth day of protests aimed at unseating Prime Minister Yingluck Shinawatra.
Protest leader Suthep Thaugsuban has appeared on television, calling for a general strike starting on Monday.
The protesters had declared Sunday "V-Day" of what they termed a "people's coup".
The anti-government activists want to replace the government with a "People's Council".
They say Ms Yingluck's administration is controlled by her brother, exiled ex-leader Thaksin Shinawatra.
Police have ordered the arrest of Mr Suthep, a former deputy PM, but so far no move has been made to detain him.
Some 30,000 anti-government protesters have gathered at about eight sites, police said.
The BBC's Jonah Fisher in Bangkok says anti-government activists have entered several TV stations and are apparently negotiating to take control of programming. He says the situation increasingly feels like an attempted coup.
The Bangkok Post reported that a group of anti-government protesters had taken control of the Thai PBS television station.
Police are holding back another set of demonstrators at the police headquarters.
Our correspondent says there is little sign demonstrators will break through there, or at Government House.
Officials denied rumours Ms Yingluck had left the country, but her whereabouts are unknown.
Ms Yingluck had earlier said the government would use minimum force to hold back the protesters.
Two people were killed and dozens more wounded on Saturday as pro- and anti-government groups clashed.
What had been largely peaceful protests turned violent when students attacked vehicles bringing pro-government activists to a Bangkok stadium. Shots were fired, but it is not clear yet by whom.
Early on Sunday, pro-government "red shirt" leaders said they were ending their mass rally at the stadium to allow security forces to police rival demonstrations.
The BBC's Jonathan Head, also in Bangkok, says military commanders have been reluctant to get involved in the conflict but agreed to deploy troops on condition they would carry no weapons and would stand behind riot police ringing the main government offices.
There is a high risk of greater violence if more supporters of Ms Yingluck - whose party enjoys strong backing outside Bangkok - try to come to the capital, our correspondent adds.
On Friday Ms Yingluck ruled out early elections, telling the BBC that the country was not calm enough for polls.
She repeated her call for negotiations to resolve the crisis.
In the past week, demonstrators have surrounded official buildings, forced their way into the army headquarters compound, cut electricity to the police headquarters and forced the evacuation of Thailand's top crime-fighting agency.
Ms Yingluck has invoked special powers allowing curfews and road closures.
Thailand is facing its largest protests since 2010, when thousands of red-shirt Thaksin supporters occupied key parts of the capital. More than 90 people, mostly civilian protesters, died over the course of the two-month sit-in.