BANGKOK - Thailand's prime minister avoided his office Monday, as thousands of protesters calling for his resignation surrounded the seat of government for the fifth day and ignored police warnings to disperse.

The demonstrators, allied with deposed leader Thaksin Shinawatra, say Prime Minister Abhisit Vejjajiva's government came to power through illegal means and should step down. Abhisit has rejected their calls.

Outside Government House, police shouted through loudspeakers: "If you don't disperse, we will use crowd control measures ranging from soft measures to harsh measures."

But the warnings only seemed to embolden the protesters gathered in the midday heat.

"Prepare yourselves for a possible crackdown," protest leader Nattawut Sai-kua told the crowd, advising them to gather wet towels and clean water to protect themselves if police fire tear gas. "But you have nothing to fear. Thousands more will join us if the police use violence."

Protest leaders called on Bangkok taxi drivers, many of whom come from rural areas that make up Thaksin's support base, to park their vehicles on heavily congested streets of the capital to paralyze traffic if authorities attempt to break up the crowd.

The protests, which began Thursday, are the latest episode in Thailand's long-running political turmoil. Last year, street rallies were dominated by Thaksin's political opponents, who besieged Government House for three months and shuttered Bangkok's two main airports for a week. They were committed to driving Thaksin's allies from power and ceased their demonstrations only after two prime ministers were removed by the courts.

The pro-Thaksin movement appeared to gain momentum outside the capital on Monday, with several hundred people rallying in at least four provinces in the north and northeast of Thailand, which remain the former prime minister's strongholds. They were seemingly responding to Thaksin's weekend call for nationwide protests. Thaksin, who was ousted in a 2006 coup, is in exile, but has been addressing the Bangkok protests via video link.

Abhisit said last week he would enter Government House on Monday. But he revised the plan, saying the situation remained under control, but he would not be going to his office before traveling to London on Tuesday for the G-20 summit, where he is representing Southeast Asian countries.

"I have not received any report of anything abnormal," he told reporters at Parliament.

Police Lt. Gen. Worapong Chiewpreecha said security officials have not been ordered to disperse the crowd. Abhisit has repeatedly said the government will not use violence.

Some government workers were relocated to a nearby government office, and others were allowed to work from home, said Jaturong Panyadilok, deputy permanent secretary of the prime minister's office.

The latest demonstrations are led by an eclectic mix of Thaksin loyalists, rural farmers and labourers.

They have vowed to use the same people-power method as their rivals to oust Abhisit, who was named prime minister by Parliament after the two Thaksin-allied governments were removed by court decisions. The protesters contend the courts were biased.

Thaksin fled into exile last year before a court convicted him in absentia of violating a conflict of interest law. The tycoon-turned-politician remains popular with the poor rural majority that benefited from his populist policies.