With troops firing tear gas ahead of the assault, the armored vehicles moved down a road toward an area where most of the estimated 3,000 demonstrators were rallying.

At least two people were shot in a gunfight in the spot where the military was coming in, one in the chest while trying to help a fellow protester. The demonstrators responded by firing at soldiers, a Reuters witness said.

Protesters ignited barricades of tires and bamboo soaked in kerosene as the military vehicles and troops arrived, causing thick black smoke to billow high over skyscrapers in the area, and camouflage thousands of demonstrators who have occupied the heart of Bangkok's commercial district for more than six weeks.

Troops earlier used bullhorns and loudspeakers to urge protesters and civilians to leave, as military helicopters circled overhead.

The military offensive came a day after the collapse of a proposal for talks aimed at ending five days of chaotic street fighting that descended into urban warfare, which killed 39 people and wounded nearly 300.

Reuters