Unions and opposition groups have called for a march on the presidential palace on Thursday, as President Omar al-Bashir rejects calls to step down after protests.

Sudan has been rocked by anti-government demonstrations that erupted on 19 December after a government decision to raise prices of bread and have since morphed into nationwide protests calling for President Bashir's ousting.

The Sudanese Professionals Association, an umbrella coalition for professional unions, said in a Wednesday statement that the peaceful march on the presidential palace will begin at Al-Qasr Avenue to "demand that President Bashir step down immediately".

The peaceful march, the association said, will start on Thursday at around 1 pm.

Protest organisers also called for demonstrations in several cities, including Madani and al-Qadarif.

Social media users have promoted the demonstrations which are expected to be confronted by security personnel.

Official estimates say 24 protesters have been killed in the demonstrations, but rights group Amnesty International has put the death toll at 40.