Hundreds of riot police have moved through parts of the Thai capital to retake areas occupied by protesters who have been demanding the resignation of the government for the past three months.
The operation in Bangkok started on Friday with police reclaiming besieged government headquarters without resistance, the Agence-France Press news agency reported.
Security forces re-took areas around Government House that Prime Minister Yingluck Shinawatra had been unable to use for about two months, according to AFP journalists, who witnessed the operation.
Most protesters appeared to have left the area already.
"Officials will return to work at Government House on Monday," Labour Minister Chalerm Yubamrung, who oversaw the move, told journalists as he inspected the building.
Yingluck and her cabinet have been forced to work from undisclosed locations around the city for weeks due to the demonstrations.
The protesters are demanding that her administration be replaced by a non-elected "people's council" which would implement reforms they say are needed to end corruption and money politics.
Protesters have battled police on several occasions, and have been targeted in several attacks for which no one has been arrested.
At least 10 people have been killed and scores injured in connection with the protests, Thailand's biggest anti-government street rallies in years.
As police entered the protest zone, they called for cooperation through a megaphone: "It is necessary for the police to clear this area ... For your own safety please strictly follow police instructions."
Slingshots and firecrackers
They then tore down tents and searched for weapons. Authorities said they confiscated slingshots, firecrackers and a variety of materials they said could be used for explosives, including a small bag of the chemical urea, metal objects and other items.
Until now, police had avoided dispersing demonstrators for fear of unleashing greater violence.
Friday's operation, which came on a national holiday when offices were closed, marked the first time in three months that police had successfully entered and cleared a protest area.
But the significance of reclaiming one street was not immediately clear given the protesters' continued occupation of several areas in central Bangkok, the Associated Press news agency reported.
Thailand has been wracked by political unrest since 2006 when Yingluck's brother, former Prime Minister Thaksin Shinawatra, was ousted by a military coup after being accused of corruption and abuse of power. Since then, his supporters and opponents have vied for power, sometimes violently.
The conflict pits the Bangkok-based middle- and upper-class and southerners who disdain Yingluck against the poor, rural majority who support her and have benefited from populist policies including virtually free health care.
In a bid to defuse the crisis, Yingluck dissolved parliament in December and called for elections that were held earlier this month. But the elections were boycotted by the main opposition Democrat Party, which backs the protesters.