Complex sentence: Other factions in the east led by Marshal Khalifa Haftar also opposed the GNA, with his forces having taken over four key oil ports but are cooperating for the moment with the GNA in allowing oil exports.
Split into simpler sentences: Other factions in the East led by Marshal Khalifa Haftar also opposed the GNA. His forces have taken over four key oil ports but are cooperating for the moment with the GNA to permit oil exports.