One report estimates that as much as 38 per cent of the population of Khartoum was infected.

The statement Thursday by Prime Minister Abiy Ahmed's office means tanks and other weaponry can now close in on the city of some half-million people.

Civilians are caught in the middle of what some experts describe as a conflict akin to an inter-state war, so heavily armed is each side.

More than 5,000 refugees arrived in Sudan's border provinces of Kassala and al-Qadarif on Sunday, the highest single-day number of arrivals since the start of the conflict in Tigray earlier this month, the UNHCR said.

Fighting that erupted in the northern Tigray region on Nov. 4 has reportedly killed hundreds on both the federal government and regional government sides and sent well over 17,000 refugees fleeing into neighbouring Sudan.

The government of Ethiopia's Nobel Peace Prize-winning Prime Minister Abiy Ahmed appeared to reject international pleas for dialogue, instead seeking to use force to arrest the leaders of a regional government it regards as illegal and destroy its well-stocked arsenal.

Reaching a negotiated settlement with rebels in Sudan's far-flung provinces has been a crucial goal for the transitional government, which assumed power after a popular uprising led the military to overthrow President Omar al-Bashir in April 2019.

Flooding caused by seasonal heavy rainfall, mostly in neighbouring Ethiopia, led the Nile River to rise about 17.5 metres late in August, the highest level it has reached in about a century according to the Sudanese Irrigation Ministry.

Years of talks between Egypt, Ethiopia and Sudan with a variety of mediators, including the Trump administration, have failed to produce a solution.

The flooding also injured two dozen people, and has destroyed or damaged more than 30,000 houses nationwide, the Interior Ministry said.