Four people, including a police officer, have been killed in Thailand and dozens wounded during clashes between riot police and anti-government protesters.
Gunfire and explosions broke out after riot police launched an operation to reclaim besieged government buildings in the capital, Bangkok.
It was the most determined effort yet by authorities to clear demonstrators from the streets since the campaign to unseat Prime Minister Yingluck Shinawatra began in November, Reuters reports.
In a day of tangled developments in Thailand's long-running political crisis, the country's anti-corruption body announced it was filing charges against the Prime Minister relating to a rice subsidy scheme that has fuelled middle-class opposition to her government.
The rice scheme, already near collapse, suffered another blow when the Government Savings said it was scrapping a loan to a state farm bank that could have been used to prop the scheme up in the face of a revolt by depositors.
The military, which has said it would intervene if police are unable to control security in the capital, has not publicly commented on the violence.
The protests are the latest instalment of an eight-year political battle broadly pitting the Bangkok middle class and royalist establishment against the poorer, mostly rural supporters of Mrs Yingluck and her billionaire brother, former premier Thaksin Shinawatra.
Reuters witnesses heard gunfire and saw police firing weapons in the Phan Fa Bridge area in the old quarter of the city. Police say they came under fire from a sniper on a rooftop and M-79 grenades were also fired.
A policeman was killed by a gunshot and several were wounded by a grenade, security officials say.
The Erawan Medical Center, which monitors hospitals, says on its website three protesters were killed by gunfire. The centre says 64 people were wounded but does not say how many were police and how many were civilians.
Security officials said earlier 15,000 officers were involved in the operation, "Peace for Bangkok Mission", to reclaim protest sites around central Bangkok's Government House and other government offices in the north of the capital.
The protesters have forced Mrs Yingluck to abandon her offices in Government House and have also blocked major intersections since mid-January.
Police say they arrested 183 people at two protest sites at the Energy Ministry, which had been cleared of protesters, and Phan Fa Bridge, and are detaining them for violating a state of emergency declared last month.
Trouble started with clouds of teargas near Government House and soon police were crouching behind riot shields as officers clashed with protesters. It was not clear who had fired the teargas and the authorities blamed protesters.
By the afternoon, police had largely withdrawn from protest sites and the streets were quiet. National police chief Adul Saengsingkaew told Reuters there were no plans to continue the operation on Wednesday.
There has been no move against the biggest protest sites in the city's commercial and shopping districts.