HONG KONG • Beijing blasted Britain for suggesting that a Hong Kong bookseller believed to be detained by China was "involuntarily removed to the mainland", accusing the former colonial power of interfering in Chinese domestic affairs.

Britain had earlier released a report describing the disappearance of Mr Lee Bo, who holds a British passport and published books critical of Chinese politics, as a "serious breach" of an agreement signed with Beijing before Hong Kong was handed back to China in 1997.

They were Britain's strongest comments yet on a case that has rocked Hong Kong, adding to growing fears that freedoms are being eroded in the semi-autonomous city.

Beijing hit back on Friday, slamming London for making "groundless accusations against China".

"Hong Kong affairs are China's domestic affairs," Foreign Ministry spokesman Hong Lei said in a statement. "We ask the British side to mind its words and actions and stop interfering in Hong Kong affairs."

MIND YOUR BUSINESS We ask the British side to mind its words and actions and stop interfering in Hong Kong affairs. CHINESE FOREIGN MINISTRY SPOKESMAN HONG LEI, on Britain's comments over the disappearance of bookseller Lee Bo. SERIOUS BREACH The full facts of the case remain unclear, but our current information indicates that Mr Lee was involuntarily removed to the mainland without any due process under Hong Kong SAR law. This constitutes a serious breach of the Sino-British Joint Declaration on Hong Kong and undermines the principle of 'One Country, Two Systems', which assures Hong Kong residents of the protection of the Hong Kong legal system. BRITAIN'S FOREIGN SECRETARY PHILIP HAMMOND, in a regular parliamentary report on Hong Kong.

Four other booksellers from the Hong Kong-based Mighty Current publishing house also disappeared in October. The Chinese authorities have confirmed they are now under criminal investigation.

But questions remain over what has happened to Mr Lee, 65, who went missing in December.

He is the only publisher to have disappeared from Hong Kong.

Letters purportedly written by Mr Lee and sent to his wife confirmed he was on the mainland, and said he had gone to China of his own volition to help with unspecified investigations.

But Hong Kong lawmakers and activists have accused the Chinese authorities of snatching Mr Lee from the city, contravening laws that do not allow mainland police to operate within the territory.

British Foreign Secretary Philip Hammond in a regular parliamentary report on Hong Kong said: "The full facts of the case remain unclear, but our current information indicates that Mr Lee was involuntarily removed to the mainland without any due process under Hong Kong SAR (Special Administrative Region) law.

"This constitutes a serious breach of the Sino-British Joint Declaration on Hong Kong and undermines the principle of 'One Country, Two Systems', which assures Hong Kong residents of the protection of the Hong Kong legal system."

Mr Hammond said Britain had called for Mr Lee's immediate return to Hong Kong and had been in communication with the Chinese government "at the highest level".

However, the Hong Kong government questioned Britain's claim that Mr Lee had been "involuntarily removed".

A government spokesman said: "Any suggestion that 'Mr Lee was involuntarily removed to the mainland' remains speculative."

Prominent pro-democracy politician Albert Ho, who has accused the mainland authorities of kidnapping Mr Lee, said Britain's comments would raise the pressure on the authorities in the city and Beijing. Washington also called on Beijing this month to explain the disappearances, with a United States State Department spokesman saying the incidents "raise serious questions about China's commitment to Hong Kong's autonomy".

Under the joint agreement, Hong Kong enjoys freedoms unseen on the mainland that are protected for 50 years, until 2047.

But there are growing fears those freedoms are under threat, with attacks on journalists and interference in the city's education institutions exacerbating concern.

Running battles between young Hong Kongers and police last week, in which 100 were injured, were a reminder of simmering tensions.

AGENCE FRANCE-PRESSE