KHARTOUM (Reuters) - Sudan's army said rebels had infiltrated into the troubled Darfur region from the Central African Republic but denied these were Islamist fighters fleeing a French advance in Mali, state news agency SUNA said on Wednesday.

With air strikes and ground forces, France has pushed Islamist rebels out of cities and into desert and mountain hideouts in a four-week operation to prevent Mali becoming a base for attacks in Africa and Europe.

Western governments fear that al Qaeda-linked fighters will cross African borders as they seek refuge.

On Friday, a Sudanese rebel group and a Netherlands-based Darfuri radio station said fleeing Islamists from Mali had arrived in the western Darfur region, scene of a decade-long insurgency.

But Sudan's army spokesman al-Sawarmi Khalid told SUNA an unspecified number of rebels based in South Sudan had entered South Darfur state via Sudan's remote border with the Central African Republic.

"These forces have nothing to do with the claims from the Darfur movements," he said.

He said the government in Khartoum had instructed the security authorities in South Darfur to destroy the rebel forces, about whom he gave no further details.

Sudan and South Sudan accuse each other of supporting rebels on each other's territory.

The neighbors, mutually deeply mistrustful after fighting one of Africa's longest civil wars, have failed to implement a September agreement to secure their disputed border after coming close to war in April.

The rule of law has collapsed in large parts of Darfur since mainly non-Arab rebels took up arms against the Sudanese government in 2003.

(Reporting by Ulf Laessing and Khalid Abdelaziz; Editing by Michael Roddy)