Three people were killed during clashes Tuesday between anti-government protesters and police in central Bangkok, authorities said.
The deadly violence in the heart of the large, bustling city is likely to intensify Thailand's bitter and protracted political crisis.
A police officer died after he was shot in the head, and two other men, aged 29 and 52, were also killed, officials said.
Fifty-eight people, both police officers and protesters, were wounded in the clashes Tuesday, according to the Erawan Emergency Center, a medical unit monitoring the unrest in Thailand.
It wasn't immediately clear if the two dead civilians were protesters.
Police were trying to clear demonstrators, who have been campaigning against Prime Minister Yingluck Shinawatra for months in central Bangkok.
After police fired tear gas in an attempt to disperse crowds of demonstrators, people among the protesters began firing guns at police.
With the two sides about 200 meters apart, police responded by firing rubber bullets and live ammunition.
During the firefight, which lasted about 20 minutes, a grenade exploded near a group of police officers, knocking them to the ground. At least four of them were wounded, said Lt. Gen. Paradon Patthanathabut, the national security chief.
Thousands of protesters
About 6,000 demonstrators were estimated to be on the streets of the city Tuesday, Paradon said, and thousands of security personnel have been mobilized.
Protesters opposed to Yingluck have been camped out since November at official buildings around the city, including Government House, the office of the prime minister and appointed cabinet ministers.
Leaders of the protests say they want Yingluck's government replaced by an unelected "people council," which would oversee electoral and political changes.
Clashes among pro- and anti-government groups had flared up during the crisis, leaving at least 10 people dead and hundreds wounded. The government responded by imposing a state of emergency last month.
But until recently, authorities had largely refrained from confronting the demonstrators directly, even when they prevented large numbers of people from voting in recent elections.
That changed last week as police began attempts to seize sites occupied by protesters for months.
Government officials said the protesters' actions were blocking public access to government services, making intervention by authorities necessary.
Officials claimed public sentiment was turning against the demonstrators. But the protesters have so far refused to give way.
The pressure on Yingluck intensified further Tuesday after Thailand's anti-corruption commission said it was bringing charges against her over a controversial rice-subsidy program.Source: CNN