The demonstrators broke into the compounds of the Department of Special Investigation and the Communications Authority in northern Bangkok -- an area that is a hub for government buildings -- and padlocked the doors to block workers from entering.
The siege came a day after hundreds forced their way into the army headquarters in central Bangkok, urging military leaders to support their campaign against the embattled premier.
Former deputy premier Suthep Thaugsuban, the leader of the protesters, declared that tomorrow would be their "victory day" and the demonstrations would be intensified even if breaking the law is required.
"We need to break the law a little bit to achieve our goals," he told protesters, who resorted to blowing whistles at the people they are upset with.
Also Read
For the past week, thousands of protesters have marched in Bangkok in a bid to unseat Yingluck, whom they accuse of acting as a proxy for her fugitive brother and former premier Thaksin Shinwatra.
Yingluck yesterday ruled out fresh polls and repeated her call for negotiations to resolve the crisis.
Deputy Prime Minister Pongthep Thepkanchana said that the demand by protesters that a "people's council" be set up was unconstitutional.