Sri Lankan security forces raided the main anti-government protest camp at the President's Secretariat here early on Friday, arresting nine people and injuring several others, as the protesters continued to occupy the sensitive area despite the resignation of Gotabaya Rajapaksa as president.

The decision to evict the anti-government protesters came a day after Ranil Wickremesinghe was sworn in as president after ex-president Rajapaksa fled the country last week.

Separately on Friday, Dinesh Gunawardena - a senior politician considered to be a long-time Rajapaksa loyalist - took the oath as new prime minister, as President Wickremesinghe tried to form a government to address the worst economic crisis faced by the island nation.

The police, with the help of three armed forces and the Special Task Force, arrested the suspects aged between 26 and 58 as it evacuated the protesters staying in the Presidential Secretariat office, its main entrance, and around the offices in the Colombo Fort, The Daily Mirror Lanka reported.

According to the police, the Crime Scene Investigation Officers (SOCO) and fingerprint analysts will be called to the President's Secretariat to obtain scientific evidence and the arrested people will be produced in court on Friday.

The police said they were investigating under the supervision of the Colombo (Central) Senior Superintendent of Police (SSP) as protesters, who blocked entry to the President's Office since April 9, said they would continue their struggle till Wickremesinghe resigned.

Police and special task force personnel forced them out on Friday when less than 100 of them were present.

The protesters had vacated the President and Prime Minister's residences and the Prime Minister's office earlier after capturing them on July 9, but they were still occupying some rooms of the President's secretariat at the Galle Face.

The protesters returned to Colombo on Wednesday after Parliament voted in six-time Prime Minister Wickremesinghe as the country's new president.

They refused to accept Wickremesinghe, 73, as the new president, holding him partly responsible for the country's unprecedented economic and political crisis.

The protesters, who had been camping at the Secretariat's gate since April 9 when they started their anti-government protest which resulted in Rajapaksa's resignation as president last week, posted on social media on Thursday that they were planning to end their protest by 2 pm on Friday.

There was a debate that we should respect the Constitution and stop this protest," said a spokesman of the group.

However, the main protest group which blocked entry to the President's Office since April 9, said they would continue their struggle till Wickremesinghe resigned.

Our victory would come only when we are able to form the people's Assembly," Lahiru Weerasekera, a group spokesman said.

Meanwhile, international concern mounted, with Ambassadors and High Commissioners posted in Colombo expressing worry over the Friday morning raid.

US Ambassador to Sri Lanka Julie Chung said she was deeply "concerned about actions taken against protestors at Galle Face in the middle of the night".

"We urge restraint by authorities and immediate access to medical attention for those injured," the Ambassador tweeted.

British High Commission to Sri Lanka Sarah Hulton also tweeted that she was concerned about reports from the Galle Face protest site.

She added in a tweet that her stance on the importance of peaceful protest was clear.

The Official Twitter handle of the European Union in Sri Lanka said the "freedom of expression" was essential to the current transition to power in the crisis-hit island nation, and added that it was hard to see how restricting the [freedom of expression] severely could help in finding solutions to the current political and economic crises.

Wickremesinghe, who was sworn in as the eighth President of Sri Lanka on Thursday, said last night that the occupation of government buildings was illegal, warning that legal action would be taken against their occupiers.

The new president said he would extend support to the peaceful protesters but would be tough on those who try to promote violence under the guise of peaceful protests.

Protesters set Wickremesinghe's personal residence on fire and occupied his office during protests last week.

Wickremesinghe has made arrangements to swear in his Cabinet on Friday at the Prime Minister's office. Such ceremonies usually take place in the Secretariat which was under the control of protesters since July 9 when Rajapaksa fled to Male before sending his resignation from Singapore last week.

Rajapaksa was forced to flee the country when a popular uprising due to his mishandling of the economy dealt the final blow. After holding on since April despite the massive protests, Rajapaksa resigned in exile in Singapore.

Sri Lanka, a country of 22 million people, is under the grip of an unprecedented economic turmoil, the worst in seven decades, leaving millions struggling to buy food, medicine, fuel and other essentials.

Schools have been suspended and fuel has been limited to essential services. Patients are unable to travel to hospitals due to the fuel shortage and food prices are soaring.

In several major cities, including Colombo, hundreds are forced to stand in line for hours to buy fuel, sometimes clashing with police and the military as they wait.

The country, with an acute foreign currency crisis that resulted in foreign debt default, announced in April that it was suspending nearly USD 7 billion foreign debt repayment due for this year out of about USD 25 billion due through 2026. Sri Lanka's total foreign debt stands at USD 51 billion.