A Buddhist monk talks to a soldier keeping watch on supporters of ousted Thai prime minister Thaksin Shinawatra at the royal plaza in Bangkok on Monday. (Chaiwat Subprasom/Reuters)

Two people were killed as violence escalated in Bangkok on Monday, with Thai soldiers using tear gas and firing weapons into the air to clear protesters calling for the resignation of Prime Minister Abhisit Vejjajiva.

The deaths, confirmed by the Erawan Emergency Co-ordination Centre, occurred during a clash between area residents and hundreds of red-shirted anti-government protesters outside the prime minister's offices.

The deaths mark the first fatalities of the protests.

Meanwhile, protesters hurled stones at police near a blockade of one of the city's main intersections Monday morning. Reuters reported some of the red shirt-clad demonstrators poured fuel on the ground and threatened to set it ablaze if police took any action.

Police then moved water cannons to the scene and fired volleys of M-16 fire into the air above the crowd, pushing back protesters. They believe Vejjajiva's four-month-old government came to power illegally and are calling for the return of ousted prime minister Thaksin Shinawatra, who has called for a revolution.

By late afternoon, most protesters were withdrawing to the area around the prime minister's office where thousands more demonstrators have been encamped since March 26. Troops appeared to be moving in after them.

"We are narrowing the area of unrest. It's going to take time, and we are trying to do cause as little loss as possible," army spokesman Col. Sansern Kaewkamnerd.

Monday's violence began before dawn as protesters commandeered public buses to block several key intersections, set tires and vehicles on fire and sent two unmanned buses, one of them burning, hurtling toward lines of soldiers in the capital.

The bus swerved and then ricocheted off trees on the side of the road before coming to a halt, with no one injured. The other bus also crashed without injuring anyone.

PM urges calm

Hospital officials say close to 100 people have been injured in Monday's violence, including two soldiers.

An emergency decree in the country bans gatherings of more than five people, forbids news reports that threaten public order and allows the government to call up military troops to quell unrest.

Abhisit, speaking in a nationally televised address just before midnight, called on the public not to panic and to co-operate to end the crisis.A supporter of former Thai prime minister Thaksin Shinawatra waves a national flag in front of a torched bus during the protest in Bangkok on Monday. (Vivek Prakash/Reuters)

"In the next three to four days, the government will keep working to return peace and order to the country," he said.

Former prime minister Thaksin fled the country last year, before a court convicted him in absentia of violating a conflict-of-interest law.

"Now that they have tanks on the streets, it is time for the people to come out in revolution. And when it is necessary, I will come back to the country," he said in a telephoned message to followers outside Abhisit's office.

The message was broadcast over a video link projected on giant screens and relayed on supporters' internet sites.

Travel warnings issued

Political tensions have simmered since Thaksin was ousted by a military coup in 2006 for alleged corruption and abuse of power. He remains popular in the impoverished countryside for his populist policies.

His opponents — many in urban areas — took to the streets last year to help bring down two pro-Thaksin governments, seizing Bangkok's two airports in November for about a week.

Canada and the United States have issued travel warnings, urging travellers to Thailand to exercise caution and monitor local media reports.

"Canadians are strongly advised to avoid locations and areas where demonstrations have been and are currently ongoing. Canadians are encouraged to verify travel schedules and services with local authorities or travel service providers prior to departure, and should exercise patience and plan accordingly."