HONG KONG, China - Police in Hong Kong sought to ban a political party which promotes independence for the city Tuesday, July 18, citing it as a potential national security threat as Beijing ups pressure on challenges to its territorial sovereignty. Semi-autonomous Hong Kong enjoys freedoms unseen on the mainland including freedom of expression but concern is growing those rights are under serious threat from an assertive China under President Xi Jinping. It is the first time such a ban has been sought since Britain handed sovereignty of Hong Kong back to China in 1997 and is the latest move to stifle any calls for independence, which have infuriated Chinese authorities. Hong Kong's secretary for security John Lee said Tuesday, July 17, he was considering the request made by police to ban the Hong Kong National Party (HKNP), a well-known but small group with a core membership of around a dozen, which promotes the city's independence from China. "In Hong Kong we have freedom of association, but that right is not without restriction," Lee told reporters. Questioned how the party was damaging national security, Lee said he could not comment on the details. However, he added that under Hong Kong law, national security meant safeguarding the "territorial integrity and the independence of the People's Republic of China". Lee said he would give the party 21 days to make representations. HKNP and rights groups said the move was a political decision to silence critics. "Today we Hong Kongers stand in opposition to our enemies, these Chinese colonizers and their puppets in the current Hong Kong government, and it is this antagonism that defines our movement," it said in a statement on its Facebook page. "This is a chilling day for freedom of association and freedom expression in Hong Kong, with potentially far-reaching consequences," said Amnesty International's Patrick Poon. The ban has been requested under the city's Societies Ordinance, which stipulates groups can be prohibited in the interests of national security and public safety. Pro-democracy lawmaker and barrister Alvin Yeung said the ordinance was first established to crack down on Hong Kong's illegal triad gangs, not political organizations. Police visit HKNP has lost momentum over the past two years as the government seeks to muzzle pro-independence sentiment. The group's leader Andy Chan told AFP police went to his home on Tuesday and handed him documents citing the requested ban, asking him to respond to the security secretary within the time limit. Chan said the documents included records of his speeches and Facebook history, adding that he thought the move may be linked to a recent trip he made to Taiwan where he spoke about Hong Kong civil and political rights at a public forum. China sees self-ruling democratic Taiwan as part of its own territory to be brought back into the fold. Pro-Beijing legislator Priscilla Leung told AFP any promotion of Hong Kong's independence by a political party was a "violation" of the city's semi-autonomous "one country, two systems" status. Activists calling for Hong Kong's independence from China emerged after mass pro-democracy rallies in 2014 failed to win reforms. But pro-independence campaigners including Chan have since been blocked from standing for office and others disqualified from the legislature. Leading independence activist Edward Leung was jailed for six years in June on rioting charges after clashes with police in 2016.