Hundreds of protesting rice farmers climbed over barbed wire fences and barricades outside the temporary offices of Thai Prime Minister Yingluck Shinawatra on Monday and threatened to storm the building if she did not come out to speak to them.
Bluesky TV also showed farmers holding signs that read ''Prime Minister Yingluck has neglected rice farmers''.
A state rice subsidy scheme that helped sweep Yingluck to power in 2011 has run into funding trouble and thousands of farmers are protesting in Bangkok, demanding to be paid.
They have mostly kept apart from anti-government protesters who surrounded her headquarters in a separate area on Monday as part of their campaign to topple her.
The farmers join thousands of protesters seeking to oust Shinawatra. The protesters have surrounded the government's headquarters, in a defiant riposte to police efforts to begin retaking sites they have been occupying for weeks.
More than 10,000 demonstrators surrounded the heavily barricaded Government House, the prime minister's main offices, and threatened to seal entrances to the complex to prevent Yingluck and other ministers from working there.
The move came as gross domestic product (GDP) data showed growth slowed sharply in the final quarter of 2013, as the political paralysis caused by months of unrest and a disrupted election began to take its toll on Southeast Asia's second-largest economy.
''We will use quick-dry cement to close the gates of Government House so that the cabinet cannot go in to work,'' Nittitorn Lamrue, leader of the Network of Students and People for Thailand's Reform, a group aligned with the main protest group, told reporters.
The protesters view Yingluck as a proxy for her elder brother, Thaksin Shinawatra, a self-exiled former prime minister who clashed with the establishment before he was overthrown by the army in 2006.
Talks between police representatives and a prominent protest leader failed on Sunday to reach a deal to reopen state offices and roads in northern Bangkok that have been occupied for months by demonstrators.
Protesters moved concrete barriers to block entrances of Government House and poured cement over the barriers in what they said was a ''symbolic gesture'' to show the building was closed. Yingluck has been forced to work from a temporary office at a Defence Ministry facility in north Bangkok since January.
NOT USING FORCE
National Security Council Chief Paradorn Pattanathabutr said troops and police were stationed inside the building to avoid a confrontation with protesters, but were not preparing to use force.
''There are enough soldiers and police inside Government House to protect the building and the grounds,'' Paradorn said.
''The protesters said they will not come inside so we aren't expecting a confrontation.''
Bluesky TV, the protest movement's television channel, showed demonstrators spilling into the grounds of the Ministry of Education, a stone's throw from Government House.
Protest leaders asked officials working there to leave the ministry, or join their movement.
Hundreds of riot police began an operation on Friday to reclaim protest sites in Bangkok and reopen roads and state offices, some of which have been blocked for more than three months.
Labour minister Chalerm Yoobamrung, who is in charge of the security operation, said police would press ahead with a plan to reclaim protest sites near Government House, the Interior Ministry, the Energy Ministry and the government administration complex in north Bangkok.
The protesters, led by firebrand former deputy premier Suthep Thaugsuban, have vowed to remain on the streets until they topple Yingluck's government and usher in political reforms before an election.
Security forces put up little resistance when protesters moved to occupy ministries and key intersections over the past few months.
The government, haunted by memories of a bloody 2010 crackdown by a previous administration that killed dozens of pro-Thaksin ''red shirt'' activists, has largely tried to avoid confrontation.
Despite that cautious approach, 11 people have been killed and hundreds hurt in sporadic violence between protesters, security forces and government supporters.
Broadly, the political crisis pits the Bangkok middle class and royalist establishment against supporters of Yingluck and her billionaire brother Thaksin, who has lived abroad since 2008 to avoid a jail sentence for a graft conviction he says was political motivated.
Demonstrators accuse Thaksin of nepotism and corruption and say he used taxpayers' money for generous subsidies and easy loans that have bought him loyalty from millions of working-class voters in the north and northeast.
An election on February 2 failed to heal a deepening political crisis. Protesters disrupted polls in a fifth of constituencies, a result that left parliament without a quorum to approve a new government leaving Thailand in political limbo under a caretaker administration with limited powers.
Voting will be held on April 27 for polling stations that were unable to open in February despite concerns raised by the country's election body that the vote may have to be scrapped and a new election called.
The protest movement has seen numbers dwindle but has experienced a second wind by trying to align itself with thousands of protesting rice farmers who haven't been paid for crops sold to the government under a state rice-buying scheme.
The country's anti-corruption body is investigating allegations that Yingluck, who is head of the national rice committee, was negligent in her role overseeing the programme.