Power's remarks came at the end of her four-day visit to Sudan, which has struggled with deep political splits and economic woes since the April 2019 ouster of strongman Omar al-Bashir.

The integration of the powerful paramilitary Rapid Support Forces (RSF) into Sudan's army has emerged as the latest challenge in the transition.

The RSF, formed in 2013 to crush rebels fighting Bashir's government, included members of Darfur's notorious Janjaweed militias, who are accused of carrying out war crimes during a conflict which left 300,000 people dead, according to the UN.

In addition, Sudan wants ex-rebel forces -- including from Darfur, who once fought both the RSF and regular forces -- to join the national army as part of a historic October 2020 peace deal.

"The United States agrees that Sudan's army should have a single and unified command," Power said in a speech at the University of Khartoum.

"We will actively support civilian-led security reform and the formal integration of the Rapid Support Forces and former opposition armed groups."

Power, administrator of the US Agency for International Development, arrived in Sudan on Saturday, meeting the country's army chief, head of state Abdel Fattah al-Burhan, and visiting Darfur.

On Tuesday, the USAID head announced $56 million of "life-saving assistance" to Sudan, and another $4.3 million to support the country's elections at the end of the transitional period in 2024.

She also said a coronavirus vaccine shipment would arrive in coming days.

Power also visited Sudan's Um Raquba refugee camp, where thousands have settled after fleeing conflict in neighbouring Ethiopia's Tigray region.

She is due to fly to Ethiopia's capital Addis Ababa, where she is expected to press officials for humanitarian access to conflict-battered Tigray, as fears grow that millions face famine there.

Ethiopian Prime Minister Abiy Ahmed sent troops into Tigray last November to detain and disarm leaders of the region's then-ruling party, the Tigray People's Liberation Front (TPLF).

Thousands have been killed, and tens of thousands have fled to Sudan.

On Monday, residents of an east Sudanese town reported seeing bodies bearing gunshots wounds or with their hands tied washing up the river on the border with Tigray.

At a Tuesday press conference in Khartoum, Power said the reports appear to be "the latest example of systematic violence carried out against civilians" in Tigray.