Emboldened anti-government protesters briefly stormed Thailand’s Parliament building on Wednesday, as lawmakers scaled the compound’s walls to flee and a Black Hawk helicopter evacuated those trapped by the encircling crowd.

“Red Shirt” protesters, following one of their most hardcore leaders, smashed through the compound’s gate with a truck and rushed into the building while Deputy Prime Minister Suthep Thaugsuban and other lawmakers were still inside. But the protesters later withdrew from the building at the request of opposition legislators.

The government security agency, known as CAPO, sent a Black Hawk helicopter carrying five soldiers armed with M-16 rifles to fly the ministers and lawmakers to safety, the agency said in a statement. INN television said Mr. Suthep was among those evacuated.

Tens of thousands of Red Shirts have been camped in Bangkok since March 12, when protests started in the historic heart of the capital. They say they will continue protests until Prime Minister Abhisit Vejjajiva, who they claim came to power illegitimately, dissolves Parliament and calls new elections.

Protests expanded to a second base on Saturday along Bangkok’s upscale shopping boulevard, where malls remained closed for a fifth day.

Mr. Abhisit had left Parliament before the break-in to attend a scheduled meeting. An aide, Sirichoke Sopa, also said the prime minister has cancelled a scheduled trip to Washington for an April 12-13 international nuclear summit.

The Red Shirts virtually have had the run of the city since Tuesday, when police and army troops made little effort to block them from triumphant, motorized rallies through central Bangkok.

The Red Shirt movement - known formally as the United Front for Democracy Against Dictatorship - contends Mr. Abhisit came to power illegitimately in the years after ex-Prime Minister Thaksin Shinawatra was removed in a 2006 coup on corruption allegations. The group is made up largely of Thaksin supporters and pro-democracy activists who opposed the putsch.

Mr. Abhisit has been under pressure to use force to restore order. But on Tuesday, he defended his government’s approach, saying in a televised address that police and soldiers were being careful to “ensure that no confrontation would spiral out of control.”

Still, some have suggested that security forces are sympathetic to the protesters’ cause and unwilling to get tough. On Wednesday, a soldier carrying an M-16 was chased out of the Parliament building by a lawmaker from a pro-Thaksin party, shouting: “This is the Parliament. Why are you carrying a gun!” Once outside, the soldier was wrestled to the ground by Red Shirts who seized his rifle and a pistol. The protesters then turned the guns over to authorities.

Many Thai columnists and editorials on Wednesday questioned whether Mr. Abhisit was losing the weeks-old confrontation with the protesters and the crucial backing of the military and police. At least four former prime ministers planned to step into the fray in an attempt to negotiate an end to the crisis, state media reports said.

“If I were the prime minister, I would have got rid of those who would not carry out my orders,” said a former head of the National Security Council, Prasong Soonsiri. He said there was strong support for the Red Shirts within the civil service and law enforcement agencies.

The storming of the Parliament was led by Arisman Pongruengrong, a former pop singer who is now one of the protest movement’s most radical leaders. Last year he orchestrated the takeover of a regional conference, forcing the evacuation of Asian leaders by helicopters and boats from a Thai seaside resort.

Local merchants have complained that the boisterous demonstrations have cost them billions of baht (millions of dollars), and many luxury hotels in the commercial centre have been under virtual siege since Saturday.

Thai authorities moved thousands of troops in riot gear on Tuesday to confront the demonstrators at their encampment in the middle of Bangkok’s tourist and shopping district. The protesters had been banned from 11 main streets, but they surged past lines of soldiers and police to parade raucously down several. A tide of red streamed through the Silom Road financial centre, with horns blaring and loudspeakers playing the folk music of rural Thailand.

The Nation, an English-language newspaper, said in a front-page editorial that Tuesday was “arguably the best day so far for the Red Shirts and definitely the worst day” for the prime minister.

“Also, for the first time, the prime minister must have started questioning the loyalty of the police and some in the military,” the editorial said.

Charnvit Kasetsiri, one of the country’s most prominent historians, called the situation “a game of brinkmanship,” with neither side wanting to be accused of initiating violence.

“It’s about who’s going to blink or make the first mistake, and whoever makes the first mistake will inevitably lose,” Mr. Charnvit said. “Both sides are very cautious. Both were worried about being the first to incite violence.”

Political turmoil has increased in the years since the 2006 coup and deeply divided Thai society. The most striking aspect may be the sense of empowerment engendered in poor rural and city people, who have long been used to kowtowing to bureaucrats and more well-off countrymen.

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