Sudan Sunday announced it had broken off diplomatic relations with Chad over a row about Chad's alleged support for rebels from Darfur launching an attack on Sudan's capital, Khartoum, dpa reported.
Sudan's President Omar al-Bashir made the announcement on television, while an overnight curfew imposed on Khartoum was extended until further notice.
Chad and the Justice and Equality Movement (JEM) rebels have both denied any cooperation in launching attacks on Khartoum's Omdurman suburb, where the rebels say they are in control - a claim denied by the Sudanese government.
Al-Bashir said in his address: "These forces are all basically Chadian forces supported and prepared by Chad, and they moved from Chad under the leadership of (rebel leader) Khalil Ibrahim."
JEM Legislative Council Chairman Eltahir Adam Elfaki, however, has insisted the group acted alone, telling the BBC from Libya that the group was "self-dependent - it is a force that built itself from the equipment of the Sudan government following our activities against the Sudan government."