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

Law, who lives in exile in the UK, 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.

Singapore's Ministry of Home Affairs noted that Law is wanted by Hong Kong authorities for charges related to national security.

Singapore has an extradition treaty with Hong Kong. A ministry spokesman stated that Law's entry would not serve the national interests of Singapore, adding that visa holders are subject to further checks upon arrival, which is what occurred with Law.

The Singaporean government has consistently maintained a cautious stance regarding foreign politics, emphasizing its refusal to allow external political influences in its domestic affairs. In a prior statement, the government expressed its commitment to opposing the importation of foreign political issues.

In a statement, Law remarked that he believes the denial was politically motivated and expressed uncertainty about possible involvement from external forces, including the People's Republic of China.

Law had applied for a visa allowing a one-time entry for a few days and had received approval three weeks prior to his trip. After the denial, he was placed on the earliest flight back to San Francisco, where he originally departed from.

The organizers of the conference he intended to attend have declined to comment on the incident. The BBC has reached out for comments from Hong Kong and British authorities as well.

Law, a former member of Hong Kong's legislature, is a key figure in the pro-democracy movement. He fled Hong Kong in 2020 following the enactment of a sweeping national security law by China that punishes various political dissent with severe penalties. In 2021, he was granted asylum in the UK.

Hong Kong authorities are actively seeking Law and others, offering rewards for information leading to their arrest. This is not the first instance where Singapore has acted against pro-democracy activists from Hong Kong.