Huang Bingzhang was this week ordained in Shantou city, under the authority of the Chinese Patriotic Catholic Association (CPCA), in the southern province of Guangdong.

The Vatican and the CPCA have been locked in a bitter struggle in recent months over control of the Catholic Church in China.

"Reverend Joseph Huang Bingzhang, having been ordained without papal mandate and hence illicitly, has incurred the sanctions laid down by canon 1382 of the Code of Canon Law," the Vatican said in a statement.

"Consequently, the Holy See does not recognize him as Bishop of the Diocese of Shantou, and he lacks authority to govern the Catholic community of the Diocese," it further said.

China's 5.7 million Catholics are increasingly caught between showing allegiance to the CPCA, or to the pope as part of an "underground" Church.

Three bishops loyal to the pope went missing or were detained recently in an apparent attempt to force them to take part in Huang's state-sanctioned ordination, their diocese members previously told AFP.

Noting the incident, the Vatican on Saturday applauded the "resistance" of the the bishops who "expressed their unwillingness to take part in an illicit ordination."

"It is meritorious before God and calls for appreciation on the part of the whole Church," the Vatican said.

The Vatican has not had formal diplomatic relations with Beijing since 1951, and in May, Pope Benedict XVI accused the country's communist authorities of pressuring Chinese bishops into separating from the Holy See.

"The Holy See reaffirms the right of Chinese Catholics to be able to act freely, following their consciences," the statement said, adding that the pontiff "deplores the manner in which the Church in China is being treated."

The guards, who worked three-hour shifts, even watched him when he showered, and the lights in his cell were kept on all night, Ai's sister Gao Ge told AFP.

Ai, an outspoken critic of the Chinese Communist Party whose detention sparked an international outcry, was released last month but has been told he cannot leave Beijing without official permission under his bail conditions.

Little has emerged about the conditions of Ai's incarceration since he was released and the artist has said he is not allowed to give media interviews as part of his bail conditions.

But his sister said Ai spent his time pacing up and down the tiny cell he was kept in.

"I don't know how many square metres the cell was, but he said he had an area of around six tiles to walk up and down," she told AFP by telephone.

"He said he walked a lot -- a distance equivalent to going from Beijing to Shanghai -- because he did not have anything else to do."

Gao said her brother, whose works have been shown around the world and who this week accepted a position with a German university, was not given access to newspapers or books during his detention, and was watched constantly.

"Two people watched him. They changed shifts every three hours and watched him 24 hours a day. They watched him very closely... whatever he did," she added.

"He said there was nothing (in the cell) -- no sunshine, no desk. Just a bed," she said.

Asked how her brother felt about his incarceration, she replied that "he accepted it", adding that he had not been tortured, but had lost a lot of weight during his time in detention.

The avant-garde artist, whose work was recently on display at London's Tate Modern gallery, was detained in April during a major government crackdown on dissidents in China and released last month.

Chinese authorities have charged Beijing Fake Cultural Development Ltd., a design firm they say is "controlled" by Ai, with evading "a huge amount of taxes".