COLOMBO, Sri Lanka — Security forces on Friday raided the protest camp at the heart of the uprising that toppled Sri Lanka’s president, breaking down tents and cordoning off large stretches of the area before dawn, in a move that could set off further unrest as the bankrupt nation seeks stability.

The protesters, many of whom were sleeping, were caught by surprise. Hundreds of police and army personnel closed off the roads leading to the protest site outside the presidential offices in Colombo, and then began clearing a wide radius around it.

The police said in a statement that they had detained nine protesters, two of whom were taken to a hospital “after sustaining minor injuries.”

Activists and protest organizers expressed shock at the raid, questioning the timing and the necessity. They had already announced that they would vacate the area by midday Friday and hand the Presidential Secretariat, the last of the buildings they had occupied, and the surrounding area back to the authorities.

“They came at 1:30 in the morning,” said Ranga Silva, one of the protesters who were present when the raid happened. “Everyone was sleeping.”

Condemnation was swift, with Sri Lanka’s human rights commission calling the raid a “brutal and despicable attack.” Diplomatic missions in Colombo, the capital, expressed concern.

“We urge restraint by authorities & immediate access to medical attention for those injured,” the U.S. ambassador, Julie Chung, said on Twitter.

The raid came a day after Sri Lanka swore in a new president, Ranil Wickremesinghe, to replace Gotabaya Rajapaksa, who fled the country this month and resigned. Protesters blamed Mr. Rajapaksa and his family, who had dominated Sri Lankan politics for years, for running the economy into the ground. The island nation of 22 million has been plagued by shortages of fuel, food and medicine in recent months.

Mr. Wickremesinghe’s rise to the presidency completed a remarkable comeback for a leader whose party had just one unelected seat in Parliament two years ago. When Mr. Rajapaksa appointed him prime minister in May, Mr. Wickremesinghe pledged support for the protest movement.

But his tone changed drastically after protesters drove Mr. Rajapaksa out and Mr. Wickremesinghe became the acting president. Protesters called for him to resign, as well, seeing him as an ally and protector of the Rajapaksa dynasty.

Mr. Wickremesinghe — whose private residence was burned down on the day of rage that forced Mr. Rajapaksa into hiding — said there were “fascists” among the protesters and promised to restore law and order, which protesters saw as a signal that a crackdown would come.

“Shameful that within a day of his election, President Ranil Wickremesinghe considered it a priority to order a midnight raid on peaceful protesters,” said Meenakshi Ganguly, the South Asia director at Human Rights Watch.

“There are the massive social and economic challenges that need to be resolved which led to the protests in the first place, something that he has been promising donors and diplomats,” Ms. Ganguly said. “And yet it appears that he wants to prove his critics right, compromise on fundamental freedoms to silence dissent.”

As the sun rose on Friday, the security forces had cordoned off the area around the presidential offices and more troops were being bused in. Lawyers and activists at the site said the police had assaulted two lawyers during the raid, while video footage showed journalists also being attacked. The BBC said one of its journalists was among those beaten.

“When we were returning from the area, a man in civilian clothes, surrounded by troops, shouted at my colleague and said he wanted to delete the videos from his phone,” said Anbarasan Ethirajan, the BBC’s South Asia editor who was reporting from the scene. “Within seconds, the man punched my colleague and snatched his phone.”

Witnesses said that the security forces had closed all the roads leading from the camp site, and that injured people were stranded there without medical assistance.

As protests condemning the raid built up in another part of the city, Mr. Wickremesinghe swore in Dinesh Gunawardena, a senior member of the Rajapaksas’ S.L.P.P. party, as the country’s new prime minister.

Skandha Gunasekara contributed reporting from Colombo, Sri Lanka, and Emily Schmall from New Delhi.