Pro-democracy campaigner says he held a valid visa and was given no reason for the refusal.

A pro-democracy activist who fled China’s crackdown on Hong Kong has been denied entry to Singapore.

Nathan Law, a former lawmaker who left Hong Kong in 2020, said he was detained and later deported to the United States after landing in Singapore on Saturday to attend a “closed-door, invitation-only event”.

Law, who is wanted by Hong Kong authorities under the territory’s national security law, said he was detained at the border for four hours before being informed he had been denied entry.

Law, who lives in exile in the United Kingdom, said he was given no reason for the refusal and was deported to San Francisco after spending about 14 hours in Singapore.

“I was granted a visa, so I was legitimately expecting an entry. I think the decision to deny entry was political, although I am unsure whether external forces, such as the PRC, are involved, directly or indirectly,” Law told Al Jazeera, referring to the acronym of China’s official name, the People’s Republic of China.

In a statement that referred to Law being wanted by Hong Kong authorities for alleged national security offences, Singapore’s Ministry of Home Affairs said the activist’s entry would not have been in the country’s “national interests.”

“A visa holder is still subject to further checks at point of entry into the country. That is what happened with Nathan Law,” a ministry spokesperson said.

The Financial Times first reported the news of Law being denied entry.

Law, a cofounder of the political party Demosisto, was among the most prominent pro-democracy campaigners in Hong Kong until a sweeping national security law introduced in 2020 effectively wiped out political opposition in the former British colony.

Since leaving Hong Kong, Law has continued to be a vocal advocate of political rights in the city and a critic of Beijing.

Hong Kong authorities issued a warrant for the arrest of Law and seven other activists in 2023, citing provisions in the national security law that allow for the prosecution of acts carried out overseas.

Once known for its vibrant civil society and political diversity, Hong Kong has dramatically curtailed dissent under the security law, which was introduced following mass antigovernment protests that began as peaceful demonstrations before descending into violent clashes between masked protesters and police.

Since 2020, authorities have eliminated opposition parties in the city’s legislature, shuttered critical media outlets, and effectively outlawed public commemorations of politically sensitive events, such as the 1989 Tiananmen Square massacre.

Beijing and the Hong Kong government have defended the crackdown as a proportionate and necessary response to the antigovernment protests and other national security threats facing the territory.