HONG KONG (Reuters) - A Hong Kong bookseller and British passport holder who disappeared last year said he had not been kidnapped by Chinese authorities, as many suspect, but had sneaked into China illegally and that he would renounce his British citizenship.

A printout showing Lee Bo, specializing in publications critical of China, and four other colleagues who went missing, is displayed outside a bookstore at Causeway Bay shopping district in Hong Kong, China January 6, 2016. REUTERS/Bobby Yip

Lee Bo, a dual British and Hong Kong citizen, and four associates went missing over the past half year, sparking fears that Chinese authorities had abducted some of the men and taken them back to China.

The disappearances provoked concern that China was using shadowy tactics to erode the “one country, two systems” formula under which Hong Kong has been governed since its return to China from British rule in 1997.

At least one of the men faces charges for selling and distributing books critical of China’s Communist Party leaders that are banned in China.

In a 20-minute interview with China’s Phoenix Television late on Monday, Lee gave the first detailed account of his disappearance from Hong Kong in December, saying he had returned to China voluntarily.

“I have always felt that I’m a Hong Kong citizen, a Chinese citizen, and because people have used my British nationality to sensationalize and make the situation more complicated, that’s why I’m deciding to give up my British nationality,” said Lee, who appeared calm in the interview.

“Why have I acted so mysteriously? It’s because I’ve had to assist with a mainland Chinese investigation and it required testifying against some people.”

Since he was afraid of reprisals from those he was testifying against, he said, “I used an illegal means to sneak there and I didn’t use my (Chinese) home return permit.”

Lee didn’t give details on how he’d crossed the border into China, or who helped him or when he might return.

“This case is quite complicated ... so I need to be questioned for longer. I am very safe and free in China. My relations with law enforcement officers are very good. They treat me very well.”

Some politicians were skeptical and said Lee may have been pressured to try to erase perceptions of Chinese authorities carrying out illegal cross-border enforcement operations.

“I don’t know who helped him sneak over... Was he forced by Chinese police or state security agents?” said James To, a lawmaker with the Democratic Party. “There is still a big question mark.”

Hong Kong Security Secretary Lai Tung-kwok said Hong Kong police would follow up to further clarify the circumstances of Lee’s case, including how he’d entered China.

Chinese Foreign Ministry spokesman Hong Lei, asked about Lee’s appearance on television, noted that Lee and his wife had already made remarks on the case many times already.

“We should respect what they have said and respect the facts,” he told a daily news briefing without elaborating.

Lee’s wife has previously said he traveled to the mainland voluntarily.

Britain said it would provide support to Lee, the BBC reported, following his latest comments. Britain has not yet been granted consular access to Lee, despite formal requests, a representative of the British consulate in Hong Kong said on Monday.

There was no immediate response from a British consulate representative in Hong Kong. Lee had been “involuntarily removed” to China, British Foreign Minister Philip Hammond said earlier.

Four of the other Hong Kong booksellers, including Gui Minhai, a Swedish national, confirmed on Chinese television on Sunday that they had been detained for “illegal book trading” in mainland China.