Twelve Roman Catholic clergymen have been detained by the authorities in northern China, according to a religious group based in the United States.
The Cardinal Kung foundation said that the priests and seminarians were in custody after attending a retreat in the city of Shijiazhuang, Hebei province, on 20 October.
"The government of China raided this peaceful retreat and arrested every one of them present," a statement by the foundation said.
A church in the vicinity was allegedly demolished several weeks earlier.
The foundation said that the detained clergymen were not part of the state approved "Patriotic Association" of churches.
China only allows its Catholics to worship in officially sanctioned groups with no ties to the Vatican.
But millions are believed to attend unofficial churches, some of which are tolerated more than others.
The president of the foundation, Joseph Kung, urged democratic countries to protest against the latest arrests and against China's suppression of religious freedom.
"All leaders of free countries should speak out against these atrocious arrests of these innocent religious believers," he said.
In July the foundation reported the arrest of five other Roman Catholic priests, also in Hebei province.
They were on their way to visit a fellow priest who had just been released from a labour camp.