Two Sudanese pastors have been detained without charge since December, according to World Watch Monitor (WWM).
Telahoon Nogosi Kassa Rata was told to report to Sudan's National Intelligence and Security Service (NISS) in mid-December, local sources report.
"He went to the NISS office behind the airport at al-Mashtel the next day, and he has been detained ever since," the source said.
Another pastor, Rev Hassan Abduraheem Kodi Taour from the district of Bahri, has also been detained since December. He was arrested alongside Rev Kowa Shamal who has been acquitted, but Taour is still being held.
No details are know of the men's location or physical health and both been are "being held incommunicado", according to WWM, a persecution watch group. Taour's lawyer has written to the Sudanese Human Rights Council to ask for help in bringing the case to court but has so far received no reply.
The Sudan Council of Churches has also written a letter to the Ministry of Religious Affairs, govermnent ministers and the Security Office to appeal for access to Rev Taour and "other Christians" believed to be held by the NISS, but has as yet also not received a response.
According to Sudanese law, an individual must either be released or presented to court 45 days after arrest. However neither event has occurred in over 60 days since Rata and Taour's arrest.
"The latest cases are representative of a much larger campaign by Sudan's government to eradicate Christianity," Sudanese religious freedom activist Kamal Fahmi told WWM.
"Since the secession of South Sudan (July 2011), Khartoum has intensified the war in Blue Nile and the Nuba Mountains (both areas of known Christian presence), and the indiscriminate harassment and arrests of church leaders and active church members" said Fahmi, who has campaigned for the repeal of Islam's blasphemy and apostasy laws.
"Foreign Christian workers have been deported. Sudan has stopped the import of Christian literature and scriptures, while confiscating most of the Christian literature in the country and closing the only Christian bookshop in the capital Khartoum," said Fahmi.
"Torture and arrest of converts from Islam is also commonplace" he added.