Khartoum - African nations launched an investigation on Monday into allegations by Sudan and South Sudan that they are supporting rebels operating in each other's territory, the African Union said.
The AU and east African bloc, the Inter-Governmental Authority on Development (Igad), launched the investigative panel in the Ethiopian capital Addis Ababa.
The three senior military officers begin work about two weeks before an 7 August deadline from Khartoum to shut down a pipeline carrying South Sudanese oil for export.
In a surprise move in early June, Sudan gave companies 60 days to stop transporting oil from South Sudan after President Omar al-Bashir accused the Juba government of backing rebels in the north.
Juba denies supporting the insurgents and in turn says Khartoum assists rebels on its soil.
Also on Monday, regional nations began determining the centreline of a demilitarised buffer zone that is to straddle the undemarcated border between the two countries.
"The launch of these mechanisms underscores the seriousness with which the African Union and Igad regard relations between Sudan and South Sudan," the AU said.
"Since 2010, Africa has been working tirelessly to promote two mutually viable states, and these current allegations threaten this objective, and in fact pose a threat to regional peace and security."