Protesters from the birthplace of an uprising that toppled Sudan's former President Omar al-Bashir were converging on the capital on Tuesday, activists said, to pressure a transitional military council to relinquish power to civilians.

The residents from Atbara, the city where the protests started on December 19, were travelling to Khartoum by train in a highly symbolic show of support for demonstrators camped at a sit-in outside the defence ministry compound.

The sit-in began on April 6, five days before the military announced Bashir's ousting. It has continued as protesters push for a swift handover to civilian rule, and the number of demonstrators has swelled in recent days.

Protests in Sudan were sparked by an attempt to raise bread prices amid a deepening economic crisis, quickly turning against Bashir's 30-year rule and spreading to major cities.

Atbara, about 290 km (180 miles) northeast of the capital, is a railway hub with a large railworker population and has historically been known to be the hotbed of opposition unions and unrest.

The TMC warned on Monday against people blocking roads and limiting the movement of citizens, signalling a possible move against thousands of protesters taking part in the Khartoum sit-in.

The TMC and the opposition have traded threats since Sunday.