AFP - Tens of thousands of Thai protesters loyal to deposed prime minister Thaksin Shinawatra were to march on an army base housing the government on Monday, as they stepped up their street campaign.

Hundreds of extra troops were deployed at the barracks on the northern outskirts of Bangkok after the protesters, decked out in their signature red shirts, told the government it must dissolve parliament or face further protests.

At least 86,000 "Red Shirts" began their rally close to ministry offices at midday on Sunday amid tight security, and gave Prime Minister Abhisit Vejjajiva 24 hours to meet their demands.

"We will leave here to listen to the government's answer at the 11th Infantry Unit," Red Shirt leader Nattawut Saikuar told reporters on Sunday. "If they fail to answer our demands we will announce our next step," he said.

The Red Shirts had dubbed their rally a "million man march" but police estimated their numbers reached only 86,000 while protest leaders said they had more than 100,000.

A 50,000-strong security force including soldiers and riot police was deployed across Bangkok and surrounding provinces ahead of the rally, under a strict law that allows authorities to ban gatherings and impose curfews.

Most of the Red Shirts were expected to leave their site for the barracks at 9:00 am, travelling by bus, car and on foot to put pressure on Abhisit and the country's top brass who are all based there during the protests.

Abhisit has rejected the calls for his resignation and cancelled a weekend trip to Australia as the rally approached.

Deputy Prime Minister Suthep Thaugsuban, in charge of the country's security, said the protesters would be permitted to approach the base but could not trespass onto it, and would not be permitted to obstruct traffic nearby.

He said it was too early to say if emergency rule would be invoked to crackdown on the rally.

"We have to see how the situation develops but I reaffirm that we will act reasonably and appropriately," Suthep said.

The Red Shirts are loyal to former prime minister Thaksin, who was ousted in a coup in 2006 and is living abroad, mostly in Dubai, to avoid a jail term for corruption. Facts: Key dates in saga of Thailand's Thaksin

Twice-elected Thaksin remains popular for his anti-poverty policies after coming to power in 2001, but he is loathed by Bangkok's establishment, which accuses him of corruption and disloyalty to the revered royal family.

Last month Thailand's top court confiscated 1.4 billion dollars of the telecoms tycoon's wealth and he addressed the crowd by video link late Sunday, urging his supporters to press on.

"I ask all Red Shirts not to give up. Don't worry about me. This is not a one-person issue, we all fight for justice. I am the victim of bullies among the elites," Thaksin said from an unspecified location in Europe.

Since the coup in 2006, Thailand has been wracked by a string of protests by the Red Shirts and their rival Yellow Shirts, whose campaign in 2008 led to a crippling nine-day blockade of the country's airports.

This rally is the largest in Bangkok since the Reds rioted in April last year, leaving two dead and scores injured.