Hong Kong's leader Tuesday refused to say why the city had denied a visa to a leading Financial Times journalist, despite escalating demands for an explanation of the unprecedented challenge to freedom of the press. Victor Mallet, the FT's Asia news editor and a British national, angered authorities in Beijing and Hong Kong by hosting a speech at the city's press club by Andy Chan, the leader of a tiny pro-independence political party, in August. Chan's party was later banned as Beijing cracks down on any pro-independence sentiment in the semi-autonomous city. An application to renew Mallet's work visa has been refused and on Sunday he was given seven days to leave Hong Kong. Facing questions for the first time since the visa denial emerged last week, Chief Executive Carrie Lam said the decision had been handed down by immigration authorities. She said linking it to the Chan talk was "pure speculation". "As a rule - not only locally, but internationally - we will never disclose, the immigration department will not disclose, the individual circumstances of the case or the considerations of this decision," Lam told reporters. She refused to directly acknowledge the specifics of the speculation over why Mallet was denied the visa, admitting only that she had "noticed there has been some talk on the street". However, Lam said the government "will not tolerate any advocacy of Hong Kong independence and things that harm national security, territorial integrity and developmental interests". She refused to comment on how Mallet could be linked to any of those potential threats when it was pointed out that he was not an independence advocate but had simply chaired a talk by Chan at the city's Foreign Correspondents' Club, which has also hosted talks by Chinese officials. Asked whether journalists could now be punished for interviewing independence activists or writing about independence, Lam said she could give no guidance but insisted that freedom of reporting and expression were "still core values". Britain and the United States have expressed concern over the visa refusal and its impact on press freedom. On Monday, a group of the city's most influential lawyers also demanded an explanation, while the American Chamber of Commerce warned that curtailing press freedom could damage the city's competitiveness. A journalists' alliance handed over petitions with more than 15,000 signatures to the government Monday calling for an explanation of its visa rejection.