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 pers.