Sudan’s interim government has cancelled more than 3,500 passports issued to foreign residents by the government of ousted President Omar al- Bashir.
The interior ministry in Khartoum said the decision was taken because of negative security reports, or because foreigners had obtained their citizenship improperly.
Sudanese media say most of those affected were from Arab countries, particularly Syria, and had paid officials $10,000 (£7,500) in exchange for citizenship.
The ministry also announced that Syrian nationals will be required in future to obtain Sudanese visas in advance of travel.
One-hundred-and-fifty-thousand Syrians are estimated to have moved to Sudan since the Syrian war began.