Respect for religious freedom in Eritrea has deteriorated over the past year, according to a United States Government report.
The Catholic Church is one of the four recognised religions
Members of unsanctioned religious groups have been harassed, detained and tortured, the State Department says.
An Eritrean Government spokesman has condemned the report, calling it inaccurate and extremely superficial.
The State Department publishes an annual report into religious freedom around the world.
Only four religious groups are officially sanctioned in Eritrea - the Orthodox church, Catholics, Muslims and the Evangelical Church of Eritrea.
In May last year it was decreed that all other religious groups should cease their activities while they awaited registration from the government.
According to the State Department report, in the 19 months since the decree, no new religious group has been recognised by the government.
For those who have secretly tried to practise their religions, the report has accounts of their alleged mistreatment.
"Some of the detainees had reportedly been rolled around in oil drums, abused by fellow prisoners and the women sexually abused," the report said.
"Some of the detainees reportedly suffer from partial paralysis and other physical injuries as a result of their torture".
The harassment was said to have continued until they recanted their faiths.
According to the report, Jehovah's Witnesses are singled out for particularly harsh treatment as they refuse on principle to perform national service.
Some were said to have been detained for more than eight years.
The incidents have been compiled from the foreign press, human rights groups, religious leaders and family members.
But Eritrea's initial response has been to question the accuracy and reliability of the sources for the report.
A government spokesman called it "scandalous and based on unreliable reports. These new extremist groups whether Christian or Muslim must abide by the laws of our country."
Yemane Gebremeskel also said contrary to the report, some religious groups have been registered and were operating in the country.
Mr Gebremeskel said: "Anybody has the full right to practise any religion but external funding for various political purposes that come under the smokescreen of religious movement are not allowed."