Sudan's military has announced plans to create a joint force to "crack down on insecurity" and assert the state's authority in the capital and nationwide as an economic crisis and regional tensions plague a fragile transition period.

The announcement was made in an order from General Mohamed Hamdan Dagalo, deputy head of Sudan's ruling sovereign council, that was published late on Thursday.

Dagalo, also known as Hemedti, is head of the Rapid Support Forces which will be part of the new force with the police, armed forces, General Intelligence Service and "representatives" of rebel groups and the public prosecutor, the order said.

In a speech this week defending reforms meant to tackle a deep economic crisis and stabilise a political transition towards elections, Prime Minister Abdalla Hamdok said there was a danger of chaos or civil war fomented by loyalists of the previous leadership.

The latest of those reforms was the removal of fuel subsidies last week at a time when annual inflation has risen to 379%, causing a public outcry.

Sudanese authorities have warned about "gangs and criminal groups" which they blame for disturbances in the capital, Khartoum, in recent days.

Sudan's Darfur region has seen an uptick in deadly violence, as has the country's eastern region, since the installation of a military-civilian power-sharing government in mid-2019.

A peace agreement signed late last year called for the integration of rebel groups into a unified national army which has not yet begun.

UN special representative Volker Perthes told a news conference he was concerned about the delay, adding that he considered the police to be best suited to protect civilians.

Dagalo's Rapid Support Forces, which emerged out of the janjaweed militias in Darfur's conflict of the early 2000s, are viewed with mistrust by many in the country.

The force announced on Thursday would be formed "immediately", under the leadership of sovereign council member General Yasser al-Atta, according to the order.

Dagalo also ordered the signatory rebel groups to get their members under control and designate gathering places. Many rebel troops had moved towards Khartoum as their leaders joined the government following the singing of the agreement.