Sudan has ordered two senior United Nations officials to leave, in what appeared to be an escalation of President Omar Hassan al-Bashir's move against UN activities in the country.
The sources identified the officials as Ali Al-Za'tari, UN resident coordinator at the United Nations Development Programme (UNDP) and Yvonne Helle, the UNDP's country director.
The reason for the expulsions was not immediately clear.
The move comes a month after Mr Bashir called for peacekeepers from the joint UN-African Union Mission in Darfur (UNAMID) to leave, calling them a "security burden".
Sudan had already shut UNAMID's human rights office in Khartoum and called on the mission to prepare an exit plan.
This comes days after denying peacekeepers permission to pay a second visit to the site of alleged mass rapes by Sudanese soldiers in Tabit, a village in Darfur, the western region plagued by conflict.
The head of the UN peacekeeping forces said UNAMID was unlikely to bow to Sudan's request to leave when the situation there appears to be worsening.
Conflict erupted in Darfur in 2003 when mainly African tribes took up arms against the Arab-led government in Khartoum,accusing it of discriminating against them.
UNAMID has been deployed in Darfur since 2007.
Both the UNDP, based in New York, and Sudan's foreign ministry declined to comment.
Contacted by email, the UNDP's Helle also declined to comment. Za'tari was not immediately available.
The sources said Helle, a Dutch national, had been told to leave Sudan by 29 December and Za'tari, a Jordanian, would depart by 2 January.