BANGKOK, Thailand - Protesters swarmed Thailand's main international airport Tuesday, forcing the cancellation of departing flights just hours after their comrades opened fire on government supporters in a clash on the streets of the capital.
It was the boldest move yet by the People's Alliance for Democracy in a monthslong campaign to topple Prime Minister Somchai Wongsawat, whom it accuses of being the puppet of a disgraced fugitive predecessor, billionaire Thaksin Shinawatra.
The protesters appeared intent on forcing the military to intervene and bring down the elected government. Army commander Gen. Anupong Paochinda has repeatedly ruled out a coup, though he has also said the army "will keep peace and order to protect the public and uphold important institutions like the monarchy."
The alliance has staged a number of dramatic actions in recent months. It took over the prime minister's office in late August and twice blockaded Parliament, one time setting off street battles with police that ended with two people dead and hundreds injured.
Tuesday's events saw for the first time the open use of guns by the alliance's so-called guards and the entanglement of foreigners: the thousands of tourists trapped at the international airport.
At another airport, which serves domestic flights, thousands of alliance protesters surrounded the government's makeshift offices.
Support for the alliance has been waning in recent weeks, and the group appeared to be edging toward bigger confrontations -- involving fewer though more aggressive followers -- in hopes of creating chaos.
"Their goal is to prevent the government from functioning. They are getting increasingly desperate in their attempt to close the deal," said Thitinan Pongsidhirak, a political scientist at Bangkok's Chulalongkorn University. "They had been losing steam and have so far failed to achieve their goal. Now, they are openly creating instability and provoking a military coup."
The anti-government protesters are mostly better educated, more affluent, urban Thais demanding that the country move away from a western-style electoral system, which they say Thaksin exploited to buy votes. They instead favour a system in which some representatives are chosen by certain professions and social groups.
They are vastly outnumbered by Thaksin's supporters in the rural majority, who delivered his party two resounding election victories. Their loyalty was sealed by generous social and economic welfare programs for previously neglected provincial areas.
The anti-government forces are well organized, and have the behind-the-scenes support of elements of the military and parties close the royal palace, the country's most influential institution.
Political tensions have been simmering since 2006, when a similar campaign against then-prime Minister Thaksin -- accused of corruption and abuse of power -- led to him being deposed by a military coup, the 18th since the absolute monarchy was abolished more than seven decades ago.
Tensions increased further with the current effort to force Somchai, Thaksin's brother-in-law, to step down. Somchai's party was the top winner in a election held in December 2007, and its coalition government is entitled to a five-year term.
Airport manager Serirat Prasutanon said the governor of Samut Prakan province, where the international airport is located, had asked the army to help police, but there was no response.
"We would like to ask the army to reinforce the police to provide security," Serirat said. Otherwise, there will be major damage to the country."
Army spokesman Col. Sansern Khaewkamnerd could not be immediately reached for comment.
Outbound flights at Suvarnabhumi Airport were temporarily suspended at 9 p.m., shortly before hundreds of demonstrators -- some masked and armed with metal rods -- broke through police lines and spilled into the passenger terminal.
The airport blockade is a fresh blow to Thailand's US$16 billion a year tourism industry, already suffering from months of political unrest and the global financial crisis. Suvarnabhumi is the world's 18th largest airport in passenger traffic, handling over 40 million passengers in 2007.
Travellers appeared bewildered by the turn of events.
"I don't know what happened to our flight," said Anna Plahn, who was seeking to return to Sweden. "They won't talk to us and I'm angry and sad because I have two small children and they're sick so we want to go home."
The protest alliance said the airport would be shut down until Somchai quits. The prime minister is scheduled to return late Wednesday from an Asia-Pacific summit in Peru and will land at a military airport, officials said.
But Deputy Prime Minister Chauwarat Chanweerakul said the government will refrain from using force to end the impasse.
"They need to stop taking over important places like airports. We will try to negotiate with them to end this siege, because it is not acceptable. It is hurting the economy, and it is hurting the country badly."
Opponents and supporters of the government clashed earlier Tuesday evening as members of the alliance returned from a rally at the smaller Don Muang airport and government supporters threw rocks at their truck. Alliance members responded by firing slingshots and a half-dozen shots with two pistols from their truck, according to footage shown on Thai PBS television.
Police Col. Piyapong Ponvanich said 11 people were wounded in the fight, most of them government supporters, some with gunshot wounds.
The clash was the second time in recent months that the two sides have fought. In a Sept. 2 clash, a government supporter was beaten to death, while two alliance members were killed last week in grenade attacks.
