By Ambika Ahuja
BANGKOK (Reuters) - Thai troops fired rubber bullets and tear gas on Saturday at demonstrators who retaliated with petrol bombs in the biggest confrontation of month-long street protests for new elections.
At least 171 people, including 64 soldiers and police, have been wounded in skirmishes near the Phan Fah bridge and Rajdumnoen Road in Bangkok's old quarter, a protest base near government buildings and the regional U.N. headquarters.
Hundreds of "red shirt" protesters also forced their way into government offices in two northern cities, raising the risk of a larger uprising against Prime Minister Abhisit Vejjajiva.
"We are changing our demand from dissolving parliament in 15 days to dissolving parliament immediately," protest leader Veera Musikapong told the "red shirt" demonstrators. "And we call for Abhisit to leave the country immediately".
Troops mounted two major offensives on protesters in the Phan Fah bridge and Rajdumnoen Road area. Both times they fired rubber bullets and tear gas to clear thousands of the protesters, who had regrouped by nightfall as troops sent in reinforcements.
An afternoon offensive ended in a tense standoff with many wounded. After dark, troops opened fire again with rubber bullets about 500 meters (1,600 ft) away at an intersection leading to Bangkok's famous Khao San Road tourist area.
"We fear sabotage by the red shirts so we are reinforcing troops on Rajdumnoen Road and the area to make sure the situation doesn't spiral out of control," army spokesman Sansern Kaewkamnerd told Reuters.
Tens of thousands also remained in Bangkok's main shopping district, a stretch of upscale department stores and five-star hotels held for a week by the red shirts.
The red shirts used taxies and pickup-trucks to barricade themselves in that area, and expanded their control to include several more blocks. Hundreds of riot police who massed at one end retreated after being surrounding by red shirts.
Into evening, many people lined the main street cheering as protesters waving red flags packed pickup trucks which streamed into the area. Some climbed up electricity poles to cover closed-circuit cameras with flags to stop police surveillance.
PROTESTS IN NORTHERN CITIES
"We are urging people to go to Pan Fah bridge for reinforcement," Nattawut Saikua, a red-shirt leader told Reuters from the shopping district. "We have a lot of people here. The situation there is much more tense."
In the shopping district, many protesters wore surgical masks and carried wet towels expecting riot police to move in with tear gas. Many were there with their families and tourists were seen walking among them.
The red shirts had vowed that they would besiege governors' offices in the provinces if there was a crackdown on their protest in the capital.
Hundreds forced their way into the governor's office compound in the northern city of Chiang Mai and hundreds more broke through the gates of a town hall in Udon Thani in the northeast.
Protest leaders made fiery speeches on a make-shift stage in Chiang Mai, calling on the government to dissolve parliament and stop the crackdown. They also rallied outside a government television station.
About 50 police were at the scene in Chiang Mai, hometown of former Prime Minister Thaksin Shinawatra, the figurehead of the red shirts who was ousted in a military coup in 2006, but did not intervene.
The government declared a state of emergency in Bangkok on Wednesday to control the protests after red shirts broke into the grounds of parliament, forcing some officials including the deputy prime minister to flee by helicopter.
The humiliating failure of security forces to stop protesters from besieging parliament and a satellite station two days later has raised questions over the competence and loyalty of Thailand's armed forces in a month of increasingly bold protests.
Writing by Jason Szep; Additional reporting by Damir Sagolj; Editing by Nick Macfie
Reuters Canada