BANGKOK, Thailand — Thousands of red-shirted anti-government protesters converged on the Thai capital Saturday, giving the government an ultimatum to dissolve Parliament or face mass marches on key spots in the city.

Although protest leaders stressed they would not resort to violence in their quest to oust the government, many businesses closed down, social events were cancelled and Bangkok's normally chaotic traffic was unusually light.

A force of 50,000 soldiers, police and other security personnel was mobilized in the capital area. A protest leader, Jatuporn Prompan, said he expected a million people to gather by noon Sunday, when the demonstration formally begins.

"If the prime minister refuses to dissolve Parliament on Sunday, we will declare new measures. We are planning to march to key spots belonging to those in power," he said. He ruled out action, however, at the Parliament building or Government House.

The "million-man march," which Jatuporn said would end Wednesday, is regarded by some as the last chance for ousted Prime Minister Thaksin Shinawatra to return to Thailand.

The "Red Shirt" protesters, formally known as the United Front for Democracy Against Dictatorship, are made up of followers of Thaksin, along with other people who oppose the 2006 military coup that toppled him.

Forcing the government out of power, Thaksin loyalists say, could pave the way for his pardon and return. Thaksin, who resides in Dubai, faces a two-year prison term for abuse of power.

Thousands of protesters arrived in the sprawling capital Saturday after travelling in trucks, buses and motorcycles from the Thaksin heartland -- the impoverished rural northeast and the north, where the fugitive leader was born.

There were no reports of violence.

In Wang Noi, to the north of the city, a line of protesters in vehicles stretched about seven kilometres along a highway as security personnel slowly searched the arrivals. Traffic jams on the highway began as far as 50 kilometres from the city.

Government spokesman Panithan Wattanayakorn said protesters were being provided with free bus rides from provincial areas to Bangkok, but vehicles driven by the demonstrators had to be parked in designated areas.

The demonstrators want Prime Minister Abhisit Vejjajiva to call new elections, which they believe will allow their political allies to regain power. They believe Abhisit came to power illegitimately with the connivance of the military and other parts of the traditional Thai ruling class who were jealous and fearful of Thaksin's popularity while in office in 2001-2006.

"As long as there is no justice, Thailand cannot be united," Jaran Ditthapichai, another Red Shirt leader, told a crowd outside police headquarters Friday. "We want power to be returned to the people."

Thailand has been in a state of constant political turmoil since early 2006, when demonstrations accusing Thaksin of corruption and abuse of power began. In 2008, when Thaksin's political allies came back to power for a year, his opponents occupied the prime minister's office compound for three months and seized Bangkok's two airports for a week.

Recent polls in Bangkok indicate a large segment of the population, irrespective of their political beliefs, is fed up with the protests, which have battered the economy, including the lucrative tourism industry.

"I'm so sick of the protests. It doesn't matter who becomes prime minister. The economy is not good and neither is anything else. Every time a protest plan is announced, tourists disappear," said Yai Oat-ngam, a restaurant owner near an area popular with foreign backpackers.

The Red Shirts have vowed to keep their protest nonviolent -- and some in Bangkok carried roses that they handed to policemen. However, the group's last major protest in Bangkok in April deteriorated into rioting that left two people dead, more than 120 people injured and buses burned on major thoroughfares. The army was called in to quash the unrest.

Many embassies have warned their citizens to stay away from areas of the city where violence could erupt.