Hundreds of mercenaries linked to Russian military intelligence have been backing the rebel commander of Libya's breakaway eastern half, The Telegraph has learned, as Moscow further expands its presence in Africa.

The murky private military company Wagner Group has been supporting Khalifa Haftar with 300 personnel in Benghazi and has supplied his Libyan National Army with artillery, tanks, drones and ammunition, a Whitehall source said.

A source close to the Libyan Russian Oil & Gas Joint Company started in Benghazi in April told The Telegraph that “lots of Wagner fighters went [to Libya], and there are rumours that military personnel also went there”.

The illegal contractors are “almost interchangeable with the GRU,” whose agents are accused of poisoning Sergei and Yulia Skripal in Salisbury, the Whitehall source said.

“They are trying to secure the deep-water ports of Tobruk and Derna for the Russian Fleet” and also “could control the flow of oil to southern Europe” if they take over Libya's energy industry, the source added.

Haftar's Libyan National Army has been seizing oilfields in a campaign that began in January. On Thursday, Haftar and the head of the internationally backed government based in Tripoli agreed in talks on the need to hold elections, although no date for the vote has been set.