In a report released in New York, the Committee for Investigation on Persecution of Religion in China published what it said were official documents outlining a campaign that includes torture to stamp out independent worship.
The report accused senior Chinese leaders of approving the violence.
The accusations come at a sensitive time for China, a week before President Bush makes his first official visit to Beijing. A Hong Kong businessman imprisoned for smuggling Bibles to a banned church was released this weekend after Bush expressed concern about him.
China's communist government allows only state-monitored worship. It is struggling to rein in new religious movements that have attracted millions of followers in recent years.
The most prominent target has been the Falun Gong spiritual movement, banned in 1999 as a threat to public safety and communist rule. But other targeted groups span the spectrum from Roman Catholics to Buddhists to newer organizations with unorthodox views.
``The level of persecution aimed against unregistered Christians in China is high,'' said the report. ``The persecution against underground Christians has escalated and originates at the highest central levels of the Chinese government.''
The committee is run by Chinese Christians living abroad.
Robin Munro, a British human rights researcher who has no connection to the committee, said he reviewed the documents that it gathered and believed they were genuine. He said it was the biggest quantity of internal Chinese government documents that he had seen assembled by one group.
``It paints a pretty frightening picture of the Chinese security authorities' attempt to suppress a wide range of spiritual groups,'' Munro said by telephone from London.
Estimates by foreign religious scholars of the number of underground, or house, church members run as high as 60 million. The official Christian churches have about 15 million followers.
The 141-page report released Monday cites documents that it said were supplied by activists in China and officials who oppose the crackdown.
They include a report that says the United States and Taiwan are using Falun Gong and other religious groups to undermine China's stability.
In addition, researchers investigated house churches in 20 provinces and found that 129 people had been killed, 23,686 arrested and 4,014 sentenced to re-education, according to the report. It didn't say how most of the deaths were alleged to have taken place or how the research was carried out.
The report accused Chinese authorities of using criminal charges against religious leaders to avoid criticism about damaging freedom of worship.
It noted the case of Gong Shengliang, founder of the banned South China Church. Gong was sentenced to death in December on charges of rape and using a cult to undermine the law, according to members of his church and human rights monitors.
According to the report, 63 other South China Church leaders have been detained and some sentenced to up to seven years in prison. It said one was missing and may have been killed.
The report cited statements by followers of other groups who said they suffered rape, beatings, electric shocks and other abuse.
The group claimed to have obtained documents showing that the harsh tactics were approved by senior leaders including Vice President Hu Jintao, who is expected to succeed President Jiang Zemin as China's next leader.