Revd Telahoon Nogosi Kassa Rata, a leader of the Fellowship of University Christian Students and a leader of Khartoum North Evangelical Church, and Revd Hassan Abduraheem Kodi Taour, a church vice-moderator, are reportedly being kept in secret locations.
The World Watch Monitor is quoting a religious freedoms activist as saying these cases represent a wider campaign by the Sudanese government to "eradicate Christianity" and the two men have no access to their families or lawyers.
The WWM reports any held from 45 days following an arrest should either be presented before a court, and the detentions of Revd Rata and Revd Taour is now unlawful.
Sudanese religious freedom activist and leader of the 'Set My People Free' website, Kamal Fahmi, told World Watch Monitor: "Since the secession of South Sudan [in 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.
"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.
"Torture and arrest of converts from Islam is also commonplace."
Revd Telahoon, 36, (also known as Telal) was reportedly summoned to a local National Intelligence and Security Service office (NISS) north of the Sudanese capital, Khartoum on December, 13, 2015.
Meanwhile, Revd Hassan Taour was detained at his home in the city of Omdurman, west of the capital and on the other side of the River Nile.
A legal representative is said to have asked to see both men but was told they were still being held by the NISS and no access to them will be given until the men are passed over for prosecution.
Revd Taour's lawyer has reportedly written to the Sudanese Human Rights Council requesting help to bring his client's case to a court of law.