Thousands of anti-government protesters blockaded Thailand's parliament, forcing new Prime Minister Abhisit Vejjajiva to delay his opening policy speech.
The red-shirted supporters of former leader Thaksin Shinawatra accuse Mr Abhisit of "stealing" power by cobbling together a coalition with former Thaksin allies two weeks ago.
The pro-Thaksin group, calling itself the Democratic Alliance Against Dictatorship (DAAD), has vowed to keep up the pressure to force a general election.
Police closed the gates of the parliament building but Mr Abhisit said force would not be used against the demonstrators.
The protests are the latest in Thailand's intractable political crisis that has seen four prime ministers this year and months of street protests.