UNITED NATIONS (AP) — The United Nations said on Friday that it's ready to assist Libya's U.N.-supported government with an investigation into at least eight mass graves discovered in territory recaptured from east-based forces commander by Khalifa Hifter.

The U.N. noted with horror reports of the uncovered mass graves, mostly in the town of Tarhuna, which have raised fears about the unknown extent of human rights violations in territories controlled by Hifter's forces, given the difficulties of documentation in an active war zone.

Philippe Nassif, Amnesty International's director for the Middle East and North Africa, said the group was working to verify the mass killings.

“We want to be able to go in, or have the U.N. go in, and collect evidence of potential war crimes and other atrocities ... so eventually a process takes place where justice can be served," he said.

Last week, militias allied with the U.N.-supported government in Tripoli recaptured the town, some 65 kilometers (41 miles) southeast of the Libyan capital, their latest in a string of battlefield successes that reversed most of Hifter's gains in the 14-month campaign to capture Tripoli.

U.N. spokesman Stephane Dujarric urged the Tripoli government on Friday “to promptly undertake the work aimed at securing the mass graves, identifying the victims, establishing a cause of death, and returning the bodies to next of kin."

The Tripoli-based ministry of justice has formed a committee to probe the causes and circumstances of the deaths.

Fathi Bashagha, the interior minister in the U.N.-supported government, said earlier this week that authorities were documenting evidence of alleged war crimes in Tarhuna, noting that preliminary reports indicated dozens of victims found in the city’s mass graves had been buried alive.

Bashagha also said that special investigative teams uncovered a shipping container in Tarhuna full of charred bodies, presumably of detainees, and blamed powerful militias loyal to Hifter that had controlled the town for “heinous crimes.” A feared Hifter-allied militia called al-Kaniyat, notorious for its targeting of dissenters, had controlled the town.

U.S. Assistant Secretary of State for Near Eastern Affairs David Schenker told reporters on Thursday that he was “troubled” by the reports that Tripoli forces had discovered bodies of civilians, in addition to landmines and other explosive devices in territory retaken from Hifter’s forces.

In divided Libya's bitter conflict, Hifter’s offensive has been backed by the United Arab Emirates, Egypt and Russia, while the Tripoli-based militias is aided by Qatar, Italy, in addition to their main sponsor Turkey.

Schenker said he sees the escalating proxy war between Russia and Turkey in Libya as a challenge to regional stability, as well as a “tragedy for the Libyan people looking for peace and and to foreign intervention.”

Libya is teetering on the brink of a new escalation as Tripoli militias wage a campaign to recapture the coastal town of Sirte, which would provide access to the country’s vast oil fields under Hifter’s control. The intensified fighting has forced nearly 24,000 people to flee their homes in the last week, according to U.N. humanitarian officials.

Despite intensified diplomatic activity to bring the sides to the negotiating table, Turkey appears keen to shore up its presence in western Libya. On Friday, Turkey’s navy and air force conducted exercises in the Mediterranean Sea near Libya, officials said, an apparent show of backing for Tripoli.

The Turkish military said the drill was meant to test and develop Turkey’s ability to command and execute long-distance operations. A government official, speaking on condition of anonymity in line with government regulations, said the maneuvers took place in international waters and airspace off Libya's coast.

The military said 17 warplanes, based in the central Turkish air base of Eskisehir, and eight frigates took part in Thursday’s “Open Sea Training.” The drill lasted for eight hours and took place along a 1,000 kilometer (625 mile) -route from the Turkish coast and back.

With Turkey’s extensive military support, including armed drones and thousands of Syrian mercenaries, the Tripoli-based forces have gained the upper hand in the conflict, retaking earlier this month the capital's airport, all main entrance and exit points to the city and a string of key towns near Tripoli.

Turkey's escalating support signals its desire to gain more leverage in the eastern Mediterranean. Ankara signed a maritime deal last fall with the Tripoli-based government that would grant it access to an economic zone across the Mediterranean, despite the objections from regional rivals Greece, Cyprus and Egypt. Turkey has said it will begin exploring for natural resources there within months.

Libya descended into turmoil in 2011, when an uprising toppled long-time dictator Moammar Gadhafi, who was later killed.

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Associated Press writer Edith M. Lederer reported this story at the United Nations and AP writer Suzan Fraser reported from Ankara, Turkey. AP writers Matthew Lee in Washington and Isabel DeBre in Los Angeles contributed to this report.