Hundreds of jihadist fighters, mainly from Sudan and Western Sahara, arrived in northern Mali over the weekend to support the Islamist groups ahead of a threatened regional intervention, witnesses and a security source told AFP Sunday.

"In the Timbuktu region and around Gao, hundreds of jihadists, mostly Sudanese and Sahrawis, have arrived as reinforcements to face an offensive by Malian forces and their allies," a Malian security official said on condition of anonymity.

One resident of Timbuktu said "more than 150 Sudanese Islamists arrived in 48 hours".

"They are armed and explained that they had come to help their Muslim brothers against the infidels," he said.

A source close to a local aid group also said that many Sudanese had arrived in the region over the weekend but added there were also fighters from other countries.

Timbuktu is one of the main cities in northern Mali, which Islamist groups have controlled since overpowering a secular Tuareg rebellion that seized the area in March.

The fabled desert city is under the control of Ansar Dine, a group led by a former Tuareg rebel leader, and Al-Qaeda in the Islamic Maghreb (AQIM).

In Gao, further east, a similar influx of foreign fighters was reported by residents.

"Since Friday, Islamists have been arriving and reporting to the Islamic police" of the Movement for Oneness and Jihad in West Africa, the AQIM offshoot that controls the city, one resident said.