BANGKOK — Four people, including a police officer, were killed and at least 64 were injured on Tuesday as antigovernment demonstrators resisted attempts by thousands of riot police officers to dislodge them from the streets surrounding the prime minister’s office.

Protesters, who are trying to overthrow Prime Minister Yingluck Shinawatra, remained defiant as the police cleared away barricades erected weeks ago to keep her and other government leaders from their offices.

“We insist that we will remain in the seized areas, because we don’t want the cabinet and prime minister to return and use their barbaric powers,” said Ekanat Prompan, a former member of Parliament who is a spokesman for the protest movement.

The government’s attempts to clear barricades, its second try within days, appeared to signal a change in approach after months of allowing the protesters to stay encamped in central Bangkok. Even after the government declared a state of emergency several weeks ago, it did not take immediate action, instead choosing to have the prime minister and other government officials work in temporary offices.