UN Secretary-General Antonio Guterres on Friday called on Sudanese authorities to investigate deaths during protests over rising food prices in Khartoum and several cities.

While the government of Sudan puts the death toll from the protests at 19, the London-based rights group Amnesty International says at least 37 people have been killed in the protests.

Guterres "appeals for calm and restraint and calls on the authorities to conduct a thorough investigation into the deaths and violence," the UN Secretary-General's Spokesman said in a statement.

The UN chief, the spokesman said, is following with concern developments in Sudan and emphasizes the need to safeguard freedom of expression and peaceful assembly.

Sudanese police fired tear gas on hundreds of worshippers who staged anti-government demonstrations after Friday prayers outside a mosque in Omdurman, as opposition groups call for more protests.

The Association of Sudanese Professionals has called for new protests against President Omer al-Bashir on 31 December, the eve of Sudan’s 63rd anniversary of independence.

Angry citizens have taken to the streets in the capital Khartoum and other cities since last week after a government decision to raise prices of bread.