LONDON (AP) — Britain's foreign secretary on Monday accused Chinese authorities of trying to silence free speech after a U.K.-based human rights group said Hong Kong police threatened it with a prison sentence and fines for allegedly violating China's national security law.

Hong Kong Watch said it received a formal warning from Hong Kong police accusing it of “seriously interfering” in Hong Kong affairs and jeopardizing China's national security by activities including lobbying foreign countries to impose sanctions against China or Hong Kong.

The letter warned that the group could face a fine of HK$100,000 (£9,800) and that its chief executive, Benedict Rogers, could face three years in prison.

The move is one of the first times that a foreigner living abroad has been targeted under China's sweeping national security law, which was imposed in 2020 as part of Beijing's increasing crackdown on dissent in Hong Kong following months of anti-government protests.

“The unjustifiable action taken against the U.K.-based NGO Hong Kong Watch is clearly an attempt to silence those who stand up for human rights in Hong Kong," British Foreign Secretary Liz Truss said in a statement.

“Attempting to silence voices globally that speak up for freedom and democracy is unacceptable and will never succeed," she said.

Rogers said his group will not be silenced by the warning and will continue to speak out for Hong Kong rights and freedoms.

Hong Kong, a former British colony that long enjoyed civil liberties and freedoms not seen elsewhere in mainland China, was promised a high degree of autonomy for 50 years when it was handed over to Chinese rule in 1997.

But in recent years Beijing has tightened its grip on the city and many have fled abroad after the introduction of the security law, which criminalizes what authorities describe as secession, subversion of state power, terrorism and foreign collusion in intervening in Hong Kong’s affairs.

Since 2020, media outlets critical of the government have been closed, the opposition has been shut out from elections and all the city’s major pro-democracy figures have either been jailed or have sought asylum abroad.