BANGKOK - Tens of thousands of supporters of ousted Thai premier Thaksin Shinawatra rallied Sunday against new leader Abhisit Vejjajiva, threatening to engulf the troubled kingdom in a fresh wave of unrest.

The red-clad protesters massed a day before Abhisit was due to give his maiden policy speech to parliament, saying they would not give up until the government that came to power two weeks ago holds fresh elections.

Most of the protesters gathered at a central Bangkok parade ground, and organisers said they would move to parliament overnight. An advance guard of several hundred had already blocked a key road outside the legislature.

"Our demand is for Abhisit to dissolve parliament because he has no legitimacy," said Jatuporn Prompan, a core leader of the pro-Thaksin movement.

Police said more than 20,000 protesters had gathered while organisers said the figure was 50,000. More than 3,000 unarmed riot police were on duty, handing out leaflets urging peaceful protests.

"Today the fight is not only for Thaksin but also for justice and democracy," former foreign minister Noppadon Pattama told the crowd.

Thaksin was ousted in a military coup in 2006 and remains in exile to avoid a jail sentence for corruption. Organisers said he might make a telephone address to the rally.