A pro-democracy campaigner who fled Hong Kong has been denied entry to Singapore despite being granted a visa, with the city-state saying his presence would not be in national interests.

Nathan Law, who lives in exile in the UK, said he arrived in Singapore on Saturday to attend a closed-door, invitation-only conference but was detained at the border for four hours.

I was not asked questions and they did not give reason for the denial, he told the BBC.

Mr Law is wanted by Hong Kong authorities who have accused him of endangering national security, Singapore's Ministry of Home Affairs noted.

Singapore has an extradition treaty with Hong Kong.

Mr Law's entry into and presence in the country would not be in Singapore's national interests, said the ministry's spokesman in response to queries from the BBC.

Singapore is known to be cautious about foreign politics. In a statement issued last year, the government said it takes a clear and strong stand against the importation of politics of other countries into Singapore.

In a statement, Mr Law said he believes the denial of entry was for political reasons. I am unsure whether external forces, such as the PRC (People's Republic of China), are involved, directly or indirectly, he said.

On Sunday, the activist was put on the earliest flight back to San Francisco, where he initially departed from.

Law, a former Hong Kong legislator, is one of the most prominent figures in the city's pro-democracy movement, having fled the city in 2020 after China imposed a national security law targeting dissent.

He was granted asylum in the UK in 2021, and his situation highlights Singapore's careful navigation of regional political dynamics.