Libya's oil minister suspended the head of the country's oil company, escalating a conflict between the two on Sunday.

Oil Minister Mohamed Oun said in a letter, confirmed by ministry sources, that National Oil Corp head Mustafa Sanallah was under investigation and had been suspended.

Oun last week said Sanallah could not act as NOC head while he was traveling overseas. He appointed Jadallah al-Awkali to run the company during Sanallah's absence.

Sanallah rejected that decision, saying there was no law that allowed Oun, who was appointed as part of the U.N.-backed Government of National Unity (GNU) that took office in March, to appoint an acting NOC chief.

The role is regarded in Libya as a sovereign position whose appointment could require agreement by other political entities such as the parliament.

NOC officials were not immediately available to comment, but the company put out a statement on an internal meeting Sanallah had held "working in a team spirit" that did not directly refer to Oun's letter.

NOC is Libya's most important economic asset, providing most public revenue even during a decade of violence and chaos that has challenged the orderly control of almost all state institutions.