Chaotic confrontations broke out in several locations, mostly involving pushing and shoving by the two sides, though some protesters wielded sticks and threw rocks, while security forces fired tear gas and rubber bullets. Reporters said live rounds were also fired, and a reporter for Thai TV station TPBS showed a spent bullet and bullet holes in the side of a car.
The so-called Red Shirt protesters are demanding that Prime Minister Abhisit Vejjajiva dissolve Parliament and call new elections. They claim that he came to power illegitimately in December 2008 with the help of military pressure on Parliament.
Government forces have confronted the protesters before but pulled back rather than risk bloodshed.
On Friday, the army failed to prevent demonstrators from breaking into the compound of a satellite transmission station. The humiliating rout of troops and riot police raised questions about how much control Abhisit has over the police and army.
Army spokesman Col. Sansern Kaewkamnerd told the Nation Channel cable TV station on Saturday that security forces will try to reclaim the rally site near Pan Fah bridge in the old part of Bangkok "before dusk." The area was occupied by Red Shirt protesters about a month ago. The government has issued an emergency decree and other orders making the demonstrations illegal.
He said that they would send more forces to a second rally site in the heart of Bangkok's tourist and shopping "to pressure the protesters." The city's elevated mass transit system known as the Skytrain, which runs past that site, stopped operations and closed all its stations as possible confrontation loomed.
The government's Erawan emergency center reported 93 people injured - mostly from tear gas or with bruises
- including 19 soldiers and 3 police officers.
"Security forces will use proper measures to take over the public areas occupied by the protesters," government spokesman Panithan Wattanayakorn told cable TV network TNN on Saturday afternoon.
The violence has not yet approached the level of last April, when Red Shirts began rampaging on city streets and torching public buses.
On Saturday, a helicopter circled over one protest site, where protesters were trying to disable public surveillance cameras by covering them with bags or cutting their cables. At a rally site in the heart of Bangkok's shopping district, protest leaders handed out damp towels and face masks to protect against tear gas, and called for more followers to gather.
The new deployment came after protesters were pushed back by water cannons and rubber bullets from the headquarters of the 1st Army Region. Although they have two main rally sites, the Red Shirts use trucks and motorcycles to send followers all over the city on short notice.
Arrest warrants have been issued for 27 Red Shirt leaders, but none is known to have been taken into custody.
Abhisit had vowed late Friday not to bend to their demands.
"It's not over yet. I'm confident if we stay true to righteousness, we will win the day," he said on nationwide television.