TUNIS (Reuters) - Forces from eastern Libya who have swept through the south and taken control of remaining oilfields in recent weeks have now reinforced a base in the centre of the country and signalled to the capital Tripoli that it may be next.

The United Nations, stunned by the southern advance, is scrambling to mediate between eastern commander Khalifa Haftar and Tripoli's internationally-recognised government led by Prime Minister Fayez al-Serraj, Western diplomats say.