The Eritrean government has released three elderly Christian men after holding them in a military prison camp and police facility.
Persecution watchdog Open Doors said that the physical condition of the men, all in their 80s, was not immediately clear.
Open Doors said two of the men were arrested last November and imprisoned in Mitire-camp, a military concentration camp in the north east of the country.
Open Doors said it believed many Christians were being held at the camp for their beliefs.
"There are some 360 prisoners held in Mitire, many of them in underground prisons or shipping containers, without enough food and medical care," the group was quoted as saying by BosNewsLife.
Another elderly Christian was also released after spending six months being held in a police station.
The three are believed to have been imprisoned due to their Christian activities. Only three Christian denominations are legal in Eritrea: the Roman Catholic Church, the Eritrean Orthodox Church and the Lutheran Church.
Other denominations are often persecuted and even those "tolerated" denominations have reported facing harassment from the authorities.
Open doors said that "especially Bible believing Christians who want to actively share their faith with others are arrested.
"Most of them are members of banned evangelical or Protestant movements."
According to Open Doors, almost 3,000 Christians have been arrested in Eritrea and are kept in what are described as "horrible circumstances," including being imprisoned in metal shipping containers.
Eritrean President Isaias Aferwerki denied that Christians were persecuted by the authorities.
"These accusations are groundless," his office said. "They are part of a routine allegation due to a lack of knowledge or done in the interest of smearing this country. So-called human rights groups pick up anything on the internet and give arbitrary figures."