Libya's internationally recognised government has formally requested from Turkey "air, ground and sea" military support to fend off an offensive of eastern forces to take the capital Tripoli, a government official has said.

It comes after Turkey's President Recep Tayyip Erdogan said earlier his country will send troops to Libya as soon as next month.

The decision puts the North African country's conflict at the centre of wider regional frictions.

Libya's internationally recognised Government of National Accord has been struggling to fend off General Khalifa Haftar's forces from eastern Libya, which have been supported by Russia, Egypt, the United Arab Emirates and Jordan.

Mr Haftar's forces were not immediately available for comment.

They have failed to reach the centre of Tripoli but have made small gains in recent weeks in some southern suburbs of the capital with the help of Russian and Sudanese fighters, as well as drones shipped by the UAE, diplomats say.

The Chinese-made drones have given Mr Haftar "local air superiority" as they can carry over eight times the weight of explosives than the drones given to the GNA by Turkey and can also cover the whole of Libya, a UN report said in November.

Last month, Turkey signed two separate accords with the GNA, led by Fayez al-Serraj, one on security and military co-operation and another on maritime boundaries in the eastern Mediterranean.

The maritime deal ends Turkey's isolation in the East Mediterranean as it ramps up offshore energy exploration that has alarmed Greece and some other neighbours. The military deal would preserve its lone ally in the region, Libya.