U.N. peacekeepers in South Sudan said on Monday that they witnessed an airdrop in the country's remote east, days after the national army accused arch-rival Sudan of arming rebels in the region.
The South Sudan army's accusation came as the two countries' presidents met in Ethiopia to work out unresolved oil and border issues and is likely to cast a shadow over any agreement made at the African Union-brokered talks in Addis Ababa.
The United Nations said it was not in a position to confirm who dropped the packages or what was in them, and Sudan has denied the charges.
The two African nations split last year under a 2005 peace deal that ended decades of civil war, but they have remained at loggerheads over a variety of issues including how to share oil wealth and who should control several disputed areas.
One of the most contentious disputes has been over mutual accusations of support for rebel groups on either side of the volatile frontier.
On Saturday South Sudan's army accused Sudan of air-dropping weapons to rebels led by David Yau Yau in the country's eastern Jonglei state, where thousands of people have died in inter-ethnic violence in recent years.
Kouider Zerrouk, spokesman for the U.N. mission in the country, said that U.N. troops witnessed a white fixed-wing aircraft drop seven or eight packages about three kilometers from the town of Likuangole in Jonglei on Saturday morning.
But he added: "The mission is not in a position to confirm who was in the aircraft or what was dropped."
Diplomats say that the talks in Addis Ababa may bring a limited deal that would open the way for landlocked South Sudan to resume oil exports through Sudan after shutting down production in January in a dispute over transit fees.
Border fighting and mistrust built up over decades of war have scuppered previous attempts to reach deals on oil and other issues.
Two million people died in the civil war between Sudan's north and south, waged for most years between 1955 and 2005 over power, ideology, ethnicity, religion and oil.
(Reporting by Hereward Holland; Writing by Alexander Dziadosz; Editing by David Goodman)