"We call on the Sudanese armed forces to talk directly with the Alliance for Freedom and Change for facilitating the peaceful process of forming a transitional government," Omar el-Digeir, a senior member of the group, said in a statement outside the army headquarters where thousands of demonstrators have massed since Saturday.

Digeir said the protest organisers had also formed a council to initiate talks with security forces and the international community aimed at agreeing a political transition that gives power to a "transitional government that represents the wish of the revolution".

"We reiterate our people's demand that the head of the regime and his government have to immediately step down."

"We also call on the Sudanese armed forces to withdraw their support for a regime that has lost its legitimacy," Digeir said, reading from a statement issued by the alliance.

"We call on the Sudanese armed forces to support the Sudanese people's alternative for a transition to a civilian democratic government."

The Alliance for Freedom and Change is an umbrella group of political parties and unions representing doctors, engineers and teachers that has led the protest movement against Bashir since December.

The rally outside the army headquarters, now in its third straight day, has been the largest since protests began on December 19 in the central town of Atbara, quickly spreading to the capital and towns and cities across the east African country.

The protesters accuse Bashir's administration of economic mismanagement that has led to soaring food prices and shortages of fuel and foreign currency.