The Vatican has strongly protested to China over the arrest of three Roman Catholic bishops - one of them 84 years old - in the past month.
Openly practising Catholics must do so in state-approved churches
A strongly-worded statement demanded an explanation from China, which has long sought to control religious expression.
Its millions of Catholics are split between followers of Pope John Paul II and members of a state-backed church.
The Vatican and China have had no diplomatic ties since the 1950s, when Beijing expelled foreign clergy.
BBC religious affairs correspondent Jane Little says the Vatican response indicates it has lost patience with China.
It called the bishops' arrest "inconceivable in a country based on laws".
"The Holy See feels deep pain for these actions, for which no explanation has been given," said Vatican spokesman Joaquin Navarro-Valls.
They breached "the rights of the person, in particular religious freedom, that are sanctioned in numerous international documents, also underwritten by the
People's Republic of China".
He said the 84-year-old bishop of Xuanhua had been arrested on 27 May and there had been no news of him for nearly a month.
The other two bishops - from Xiwanzi and Zhengding - were taken into custody for several days this month and released.
None were further identified.
The Vatican says about eight million Chinese belong to the so-called underground Catholic church, while the state-backed Chinese Patriotic Church has an estimated five million members.
In December, Beijing dismissed an official American report which had criticised religious intolerance in China.