NATO allies called on parties to the conflict in Libya to immediately abandon any hostile action that may jeopardize energy infrastructure and oil exports.

The governments of France, Germany, Italy, Spain, the United Kingdom, and the United States expressed concern about weekend attacks on oil terminals in Libya.

"We call on all parties to undertake an immediate ceasefire and to refrain from any further hostilities," they said in a joint statement. "We also call on all forces to avoid any action that could damage Libya's energy infrastructure or further disrupt its exports."

Forces loyal to a Libyan military leader in the east of the country gained leverage over four oil ports, driving out an armed unit backed by the government in Tripoli, which has the support of the United Nations.

Martin Kobler, the U.N. special envoy for Libya, said military action in oil terminals was in violation of U.N. Security Council resolutions dealing with the security of energy infrastructure in the country. Attacks on oil installations, he said, could widen the gap between rival power structures in Libya and led to great instability in a country torn in half by civil war.

NATO allies said all warring parties in Libya should unite to fight against militants loyal to the terrorist group calling itself the Islamic State. While the oil infrastructure, production mechanisms and export volumes remain under control of the government, "Libya's oil belongs to the Libyan people."

Libya's political environment fractured in the wake of civil war in 2011, with factions establishing authority from opposite sides of the country. The country in July moved to reopen some of its oil terminals, which were idled for nearly two years by threats from rival internal powers.

Libyan oil production declined nearly 7 percent from July to August and is more than 70 percent less than peak levels before the outbreak of civil war.