Thai police Friday forced their way through protesters to enter a government building in a compound that anti-government protesters seized Tuesday.
Police said they were not there to disperse the demonstrators, although protest leaders claimed they were.
"We are not dispersing the crowd. Police did not use force on protesters because this is a sensitive matter," deputy police spokesman Major General Surapol Thuanthong said.
Chamlong Srimuang, a People's Alliance for Democracy (PAD) leader and retired army general, thought different and told other protesters the police were trying to disperse the crowd, reported dpa.
Surapol said that was not true and "blood will not be shed."
The confrontation comes on the fourth day of a standoff between anti-government protesters led by the PAD and the government.
Prime Minister Samak Sundaravej said Thursday that police would not use force to remove anti-government protesters who seized and have held the government compound, but Friday's move seems to have upped the ante.
Thursday evening the number of protesters swelled to an estimated 20,000 or more, but their numbers dwindled after a torrential rain storm during the night.
Thailand's criminal court has ordered the protesters to disperse from the compound around Government House and issued arrest warrants for nine leaders of the PAD, which is spearheading the demonstrations.
The court issued the nine warrants Wednesday for "treason" and had threatened to serve them Thursday, but Samak said police would not break through the crowd of supporters to arrest the PAD leaders and instead would give them a chance to surrender to authorities.
Tens of thousands of PAD supporters seized several government buildings early Tuesday and held them most of the day until they converged near the prime minister's compound Tuesday evening.
Chamlong said the protesters want to block the government from amending the 2007 constitution and pressure the administration to resign.
Earlier, Samak said his government would not be forced from power because it had been legally elected.
Two years ago, PAD organized months of protests against former prime minister Thaksin Shinawatra, who was eventually ousted in a bloodless military coup in September 2006.
The PAD and coup leaders charged Thaksin with massive corruption, dividing the nation and undermining democracy and the monarchy.
The PAD is now trying to bring down the government of Samak, a political ally of Thaksin who openly campaigned as a proxy for him.
It has been calling for Samak's resignation since May after the cabinet approved a motion to amend the 2007 constitution. Protest leaders charged the amendments are aimed at clearing Thaksin of corruption charges and paving the way for his return to power.
Thaksin, a former policeman turned billionaire businessman, was prime minister from 2001 to 2006, winning a huge following among Thailand's rural poor.
But the populist politician drew the opposition of the political elite when his growing power led to perceived abuses for personal gain.
After spending 17 months in exile in the post-coup period, Thaksin returned to Thailand in February but fled again this month after his wife was convicted of tax evasion charges. She skipped bail, and the couple is now seeking asylum in Britain.
With Thaksin now seeking asylum overseas, the PAD has lost one of its biggest drawing points, and some analysts said they think the momentum of the protests will dwindle.