The Sudanese army early on Thursday warned of what it described as a "mobilisation of forces and redeployment" by the powerful Rapid Support Forces (RSF) in the capital Khartoum and other cities.
The army in a statement said the RSF's movements represent a "clear violation of law".
The statement represents a rare public rebuke to the RSF, a paramilitary group that operates in Sudan under a specialised law and with its own chain of command.
The RSF said in an earlier statement that it deploys across the country as part of its normal duties.
(Reporting by Khalid Abdelaziz; writing by Hatem Maher; editing by Jacqueline Wong and Michael Georgy)