Forces loyal to east Libyan commander Khalifa Haftar on Sunday seized at least two key oil ports from a rival force loyal to the U.N.-backed government, risking a new conflict over the OPEC nation's resources.

Ahmed al-Mismari, a spokesman for Haftar's self-styled Libyan National Army (LNA), said its fighters had full control of Es Sider, Ras Lanuf, Brega and Zueitina after launching an early morning military operation on the eve of the Muslim holiday of Eid.

The attacks on Libya's major oil ports by Haftar, who opposes the U.N.-backed Government of National Accord (GNA), could derail efforts to restart production. Those efforts are seen as critical to saving Libya's economy and helping the GNA survive.