The Hong Kong media tycoon and pro-democracy campaigner Jimmy Lai has been denied bail, after being charged with colluding with foreign entities under the city’s new national security law. Lai, who marked his 72nd birthday in jail this week, appeared in court on Saturday handcuffed to a chain around his waist, and led by a police officer. He was charged on Friday with offences including asking foreign countries to impose sanctions on Hong Kong or China, and taking other “hostile action”, local media sources – including his own newspaper, Apple Daily – reported. The charges are reportedly based on things he has tweeted and commentaries he has published, as well as interviews with foreign media. Some of the acts flagged by police were committed before the national security law came into force. They include a tweet from May asking Donald Trump to sanction Chinese officials, and his decision in June to launch an English-language edition of Apple Daily, the paper said. The presiding judge adjourned the case until 16 April to allow prosecutors more time to sift through Lai’s Twitter account and other evidence they cited in the hearing, the South China Morning Post reported. He was denied bail on the grounds that some alleged offences in the current case had been committed while Lai was awaiting trial on other charges, so he faces at least four months in pre-trial detention. After Lai was charged on Friday, the US vice-president, Mike Pence, tweeted his support, calling him a “hero” and referring to the charges as “an affront to freedom-loving people everywhere”. The US secretary of state, Mike Pompeo, called for Lai’s immediate release. Lai is the most high-profile figure targeted under the sweeping national security law passed this summer by Beijing, after more than a year of street protests that had morphed into a broad pro-democracy movement. The law allows Chinese security forces to operate from Hong Kong and has effectively curtailed the limited autonomy which the city was meant to enjoy until 2047, under the terms of the 1997 handover from British colonial rule. It has been used against pro-democracy politicians, the media, protesters and academics. Lai was first arrested after police raided the offices of his media company in August, but released on bail. In early December, when he reported to a police station under the terms of his bail agreement, he was arrested and held on fraud charges. The national security law’s harsh penalties mean that if convicted, Lai could spend the rest of his life in jail. It sanctions life imprisonment for broadly defined crimes of secession, subversion, terrorism and collusion with foreign forces.