Hong Kong bookseller Lee Bo who disappeared from the city and surfaced in mainland China has returned, police said Thursday, the latest twist in a case that has provoked anger over China's interference in the city.

British citizen Lee is one of five Hong Kong booksellers known to go "missing" in recent months -- the other four are now under criminal investigation on the mainland.

The men all worked for the Mighty Current publishing house in Hong Kong, which produced salacious titles about political intrigue and love affairs at the highest levels of Chinese politics.

Lee's case caused the greatest outcry because he disappeared from Hong Kong, prompting accusations that Chinese law enforcement agents were operating in the semi-autonomous city, which is illegal under its constitution.

The other four booksellers went missing from Thailand or southern mainland China.

"Immigration department and police met and took statement separately with Lee Bo, who had returned to Hong Kong from the mainland this afternoon," a government statement released late Thursday said.

Lee had been handed over to immigration officials at the Lok Ma Chau border point in northern Hong Kong, the statement said.

Lee, 65, was last seen at a Hong Kong book warehouse before his disappearance, but spoke publicly for the first time on Chinese television late last month saying he had gone to the mainland of his own accord.

Britain however had said in February it believed he had been "involuntarily removed to the mainland" in what it described as a "serious breach" of an agreement signed with Beijing before Hong Kong was handed back to China in 1997, a deal that protects Hong Kong's freedoms for 50 years.

That earned the ire of Beijing, which blasted Britain for interfering in its domestic affairs.

Thursday's government statement again insisted Lee had "returned to the mainland by his own means voluntarily and it was not an abduction".

- 'Crushed confidence' -

Lee told police he was assisting an investigation into fellow bookseller Gui Minhai, the statement added.

"He stated that he was free and safe whilst on the mainland," it said.

Lee requested the cancellation of his missing person case and said he did not require assistance from the Hong Kong government or police, the statement added.

Immigration officials also took a statement from Lee, adding he did not provide "thorough information" about his departure and that they would further investigate whether he had committed any immigration offences.

Lee "left on his own" after meeting police, the statement said.

Lee, speaking at the border, told Phoenix TV that "coming back to Hong Kong and being able to see my relatives and my son who I haven't seen for a long time makes me very happy".

Denying that Chinese security agents had smuggled him out of Hong Kong, he said that he returned using "normal means because I have made good progress in terms of my assistance in the investigation".

I feel there is a possibility that I may need to return to the mainland multiple times to assist in the investigation."

He added:

"I won't smuggle myself back in (to China) again".

Critics said Lee's return would not restore confidence.

"The Lee Bo incident has really crushed the confidence of Hong Kong people in respect of 'One Country Two Systems'," pro-democracy lawmaker Albert Ho told AFP, referring to the semi-autonomous deal under which the city is governed.

"Nobody really believes (Lee's) version. People have the general impression that he was forced to go back to China."

China expert and Chinese University of Hong Kong professor Willy Lam said he believed a condition of Lee's release would be that he did not "spill the beans about the circumstances of his abduction to China".

The other four booksellers are under criminal investigation on the mainland.

Swedish citizen Gui Minhai confessed to trying to smuggle illegal books into China in a television interview in February.

Cheung Chi-ping, Lui Por and Lam Wing-kee blamed the company's illegal book trade on Gui.

Cheung and Lui returned to Hong Kong earlier this month on bail, but are reported to have quickly returned to the mainland.

The case has drawn international criticism, with the European Parliament calling for the immediate release of all five men.