Anti-government protesters have burst into the control tower at Thailand's main international airport as part of a demonstration that forced the cancellation of all of Wednesday's flights.

Officials say the protesters are trying to get information on the flight plans for Prime Minister Somchai Wongsawat.

Mr. Somchai had been scheduled to arrive at Suvarnabhumi international airport from an international summit in South America (Asian Pacific Economic Conference) Wednesday.

Protest leaders, with the People's Alliance for Democracy, say the blockade of the airport is part of a "final push" to topple the prime minister and they will not enter into any talks until he steps down.

Thai military officials called an urgent meeting Wednesday with government officials, academics and business leaders to discuss possible solutions.

The protest has stranded thousands of travelers at the airport.

Earlier, a small blast injured several protesters at the international airport, and authorities in Bangkok say unknown assailants threw grenades at anti-government protesters at a domestic airport Tuesday.

The airport siege followed a violent clash earlier Tuesday, during which anti-government protesters chased government supporters on a major highway in the capital, Bangkok.  At least 11 people were wounded during the street fight, some with gunshot wounds.

The blockade of Thailand's main airport could damage the country's already fragile tourism industry.  Singapore Wednesday urged its citizens not to visit Thailand due to the uncertain political situation.  And the United States, Britain and Australia have urged their citizens to take extra precautions if they planned to make the trip.

Protests in Thailand intensified on Monday when opposition supporters forced parliament to delay a session by blocking access to the building.

Protesters accuse Mr. Somchai of being a proxy for Thaksin Shinawatra, his brother-in-law, who was ousted in a military coup in 2006 for alleged corruption.

Some information for this report was provided by AFP, AP and Reuters.