Leaders of tens of thousands of protesters who swarmed into Bangkok from Thailand's rural areas threatened mass street demonstrations if the government didn't respond to their demand for a dissolution of parliament within 24 hours.

The demonstrators, popularly known as the Red Shirts, want Prime Minister Abhisit Vejjajiva to call new elections, which they believe will allow their political allies to regain power.

They believe Mr 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 former Prime Minister Thaksin Shinawatra's popularity while in office from 2001 until he was ousted in a 2006 coup.

"We're demanding the government give up the administrative power by dissolving the Parliament and returning power to the people," a protest leader, Veera Musikapong, told a sea of red-shirted followers. "We're giving the government 24 hours from now (to respond to our demand)."

The protesters said they will march on key locations in the city if the government fails to respond by noon on Monday.

These are to include the headquarters of the 11th Infantry Regiment, where Mr Abhisit has been living in recent days.

In his weekly radio address Sunday morning, Mr Abhisit indicated he had no plans to dissolve Parliament.

"Dissolution and call for resignations are normal in a democratic system. But we have to make sure the dissolution of Parliament will solve the problem and won't make the next election troublesome," Mr Abhisit said.

He also denied rumours that a military coup was possible and said he would not impose a state of emergency that would give the army broad powers to deal with the protests.