With oil again acting as kindling for conflict in Libya, the U.N. mission there reminded all parties to respect the sanctity of the nation's economic lifeline.

Martin Kober, the U.N. special envoy for Libya, said Wednesday he was deeply concerned by attacks on oil installations carried out by the Islamic State terrorist group.

"It constitutes a grave assault not only on the lifeline of Libya's national economy, but on the very livelihoods of millions of ordinary Libyans, many of who are already enduring hardship as a consequence of the ongoing political and military conflict in Libya," he said in a statement.

Attacks on Libyan oil installations are nothing new. Last year, U.S. oil company Marathon said there was "considerable uncertainty" surrounding any future production in Libya.

The Organization of Petroleum Exporting Countries reported member-state Libya produced about 345,000 barrels of oil per day last month, a 10 percent decline from the previous month. Before conflict erupted early in the decade, Libya was producing more than 1 million bpd.

Libya's political environment fractured in the wake of civil war in 2011, with factions establishing authority from opposite sides of the country. Kobler last month praised the seating in Tripoli of a U.N.-backed national administration. An eastern administration tested the patience of the international community when it shipped a cargo of oil from the Hariga port.

In his statement, Kobler said all parties in Libya were called on to respect the authority of the U.N-backed administration over the nation's resources.

The U.N. Support Mission in Libya pointed to a March resolution from the U.N. Security Council that condemned illegal oil exports, "including by parallel institutions which are not acting under the authority of the government of national accord, and underlining the primary responsibility of the government of national accord in taking appropriate action to prevent the illicit export of crude oil from Libya."

A March report from Transparency International said that, while oil is important to the Libyan economy, it's also a source of potential corruption. "Immense sums of money" are being managed without any significant level of transparency, the report said.