Sudan is expelling the country directors for two foreign aid groups, accusing them of violating a ban on engaging in political activities.
The British charities Oxfam and Save the Children received letters warning of the expulsion orders, and said they plan to follow up with Sudan's government.
The United Nations is pressing Khartoum to reverse the orders, saying the aid groups play a key role in helping victims of fighting in western Sudan.
Sudan's government has criticized the groups for issuing statements which it says indicate support for the rebels in the western Darfur region.
It also rejected a Save the Children press release that accused Sudanese troops of bombing a site near a refugee camp in the town of Tawilla earlier this month.
Some information for this report provided by AFP, AP and Reuters.