Sudan's SUNA news agency had said Sunday that the weapons were seized by customs and an investigation launched after they were flown in on an Ethiopian Airlines passenger flight.

SUNA quoted officials as saying the weapons had originally been sent from Russia to Ethiopia in May 2019 and were held by authorities there for two years.

"There are suspicions that they were meant to be used in anti-state crimes, to impede the democratic transition, and prevent transition to civilian rule," SUNA reported.

Sudan has been undergoing a rocky transition since the April 2019 ouster of president Omar al-Bashir following mass protests against his rule.

But Ethiopian Airlines, the biggest carrier in Africa, said it had full documentation to prove the legality of the shipment including a letter from Sudan's foreign ministry.

"Ethiopian Airlines' shipment of weapons to Sudan is a legal and commercial transportation of hunting guns with all proper documents of the shipper and the consignee," it said in a statement.

It said the guns had been held by security authorities in Addis Ababa for a long time for verification, and that the recipient had sued the airline in a Sudanese court to either deliver them or pay almost $250,000 compensation.

Relations are frosty between Khartoum and Addis Ababa, with the two countries at odds over the Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile and Ethiopian farmers' use of a fertile border region claimed by Sudan.

Last month Sudan recalled its ambassador to Ethiopia, saying Addis Ababa had spurned its efforts to broker a ceasefire in the Tigray conflict.

Tens of thousands of refugees from the 10-month war in the northernmost region of Ethiopia have been crossing the border into Sudan.