Thousands of Thai riot police are clearing areas of Bangkok where anti-government protesters have set up camp for weeks.
There were no reports of clashes in the Friday police operations to clear the Government House and other official buildings.
Baton-wielding, helmeted police removed tents and barriers belonging to the protesters, who were warned through loudspeakers not to resist.
But Issara Somchai of the opposition People's Democratic Reform Committee suggested many protesters will not back down easily.
"No return. Every place (that's been occupied) will not be given back. If the police want to disperse us, I believe there will be a confrontation."
Police say they are searching the areas for weapons, and accuse many of the protesters of gathering illegally.
Chalerm Yubumrung, who is leading the police operation, told protesters that if they do not leave, the law will be "gently enforced."
Authorities last month announced a state of emergency and have put out arrest warrants for many of the protest leaders.
But until now, police had largely allowed the demonstrations, which blocked intersections and sometimes occupied government compounds.
The opposition protesters are trying to force Prime Minister Yingluck Shinawatra from power, saying her government is hopelessly corrupt.
Clashes and small-scale attacks on protesters have killed at least 10 people since November, Thailand's worst political violence since 2010.
Ms. Yingluck had hoped early elections, held February 2, would help resolve the crisis, which has gripped the country since November.
But the opposition Democratic Party boycotted the vote. Many opposition protesters also disrupted voting in several provinces.
The ruling Pheu Thai Party is thought to have won the election, but results cannot be announced until another round of voting is held.