Sudan is likely to have supplied weapons by air to rebels battling the government in neighbouring South Sudan, a report released Tuesday said, despite Khartoum's denials of involvement in the conflict.
The study from the London-based small arms research organisation, Conflict Armament Research, documented a cache of weapons and ammunition captured by South Sudanese government troops from the rebels in Jonglei State in November.
"The composition of the documented materiel, and a precedent for airdropping identical materiel to rebel forces in South Sudan in 2012, prior to the current conflict, suggests direct supply from Sudan to SPLM-iO (Sudan People's Liberation Movement-in-Opposition) forces," the report said.
The report said rifle ammunition had been damaged in a way that suggested it had been dropped from an aircraft, with photographs showing what the research body said were Sudanese manufacturers' marks.
The 7.62x39 mm ammunition -- bullets used in Kalashnikov-style assault rifles -- had "lateral impact damage, which is consistent with either free-fall dropping from an aircraft or very low altitude parachute dropping."
Some 70 percent of this particular type of rifle round were made in Sudan in 2014, the report said.
"The recent date of manufacture is further evidence of direct supply from Khartoum to SPLA-iO forces," the group said.
It added that the equipment they had seen "mirror weapons types that Sudan has supplied to support armed or insurgent forces elsewhere in sub-Saharan Africa, including in Darfur and the Central African Republic."
Other ammunition seen by the team originated in China.
South Sudan split from the north in 2011 under a peace deal that ended a bloody 22-year civil war, but relations between the countries have been tense since then.
Khartoum has repeatedly denied that it is involved in the civil war in South Sudan, which has pitted President Salva Kiir against his arch rival and former deputy Riek Machar since December 2013.
Khartoum has also accused South Sudan's government of backing rebels battling in its border regions.
Fighting in South Sudan has worsened in recent weeks, with the UN and aid agencies saying millions of people are going hungry.
Several rounds of peace talks between the rebels and the government have done little to put an end to the conflict.