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 its 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 hours before he was deported.

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

Mr. Law, who also previously served as a local legislator in Hong Kong, is one of eight exiled activists wanted by the city's authorities who have accused him of endangering national security.

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.

'A visa holder is still subject to further checks at point of entry into the country. That is what happened with Nathan Law,' added the spokesman, citing 'questioning and immigration and security assessment'.

The government had previously stated it 'takes a clear and strong stand against the importation of politics of other countries into Singapore'.

In a statement, Mr. Law expressed belief that the denial of entry was for 'political' reasons and questioned whether external forces, such as the People’s Republic of China, were involved.

Law holds a UK Refugee Travel Document and had confirmed that he applied for a visa that permitted a 'one-time entry for a few days', approved three weeks prior to his travel. Following his denial, he was placed on the earliest flight back to San Francisco.

The event's organizers have declined to comment, and a spokesperson for the Hong Kong government emphasized that each jurisdiction manages immigration based on its own laws.

Law, a key figure in the pro-democracy movement, fled Hong Kong in 2020 due to a stringent national security law imposed by China. He was granted asylum in the UK in 2021, with authorities in Hong Kong offering rewards for his capture. Singapore's action against Law reflects ongoing tensions involving exiled activists from Hong Kong.