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 who is 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, said the spokesman, adding that Mr Law was referred for questioning, and immigration and security assessment after he landed.

The government had previously 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. Mr Law said he applied for a visa that would have allowed him a one-time entry for a few days, and that it was approved three weeks before his departure. He said he holds a UK Refugee Travel Document.

On Sunday, the activist was put on the earliest flight back to San Francisco, where he initially departed from. A Hong Kong government spokesperson said that it is a basic legal principle that each jurisdiction shall handle immigration matters in accordance with its own laws and urged Mr Law to return to Hong Kong and surrender to rectify his wrongdoing. The backlash against Mr Law also saw Chinese officials labeling him as an anti-China troublemaker.

This incident raises questions about Singapore's stance on exiled activists and its diplomatic relations with Hong Kong and mainland China, especially following previous instances of actions taken against pro-democracy figures.