The Vatican accused China on Wednesday of violating human rights, stepping up its criticism of the communist government for what it sees as the repression of religion.

A strongly worded Vatican protest demanded that Chinese authorities explain why three bishops had been arrested in the past month. The arrests "violate those human rights, in particular the right to religious freedom, which are protected by numerous international documents to which the People's Republic of China has adhered," the Vatican statement said.

The chief Vatican spokesman, Joaquin Navarro-Valls, said in the statement that there had been no word of the 84-year-old bishop of the city of Xuanhua, in Hebei province, since he was arrested on May 27.

He said the bishop of Xiwanzi, also in Hebei, had been placed in detention for 10 days this month and the bishop of the northern city of Zhengding had been detained for five days. The statement did not name the bishops.

"The Holy See feels deep pain over these measures, for which no explanation has been given," the statement said. "They are inconceivable in a country based on laws."

China does not allow its Roman Catholics to recognize the authority of the pope and compels Catholics to belong to state-backed patriotic associations if they want to worship openly. Those who refuse worship secretly and are considered members of the underground church.

The Vatican estimates it has about 8 million followers in China, compared with about 5 million who follow the state-backed Chinese Catholic Patriotic Association.