CAIRO (AP) — A leading rights group on Thursday urged Libya's U.N.-backed government to investigate the fate of hundreds of people missing from a key town near the capital, Tripoli. Dozens of mass graves were found there after the withdrawal of a much-feared militia last summer.

In a statement, Human Rights Watch quoted Libyan officials as saying that at least 338 residents of the town of Tarhuna were reported missing. The majority of them disappeared during a 14-month-long military campaign led by forces loyal to a rival government, based in eastern Libya, to capture the capital, according to the report.

Since 2015, Libya has been divided between two governments, the U.N.-supported one based in Tripoli and the one in the east, each backed by a vast array of militias.

In April 2019, east-based commander Khalifa Hifter and his forces marched on Tripoli in an attempt to take the city and tried to co-opt some rival militias. At the time, the town of Tarhuna was under the control of the notorious al-Kaniyat militia, which had initially sworn allegiance to the Tripoli government.

But the militia changed sides in 2019, siding with Hifter and granting his troops access to Tarhuna, a strategic town some 65 kilometers (41 miles) southeast of the Libyan capital. Since then, the Tripoli government has discovered 27 mass graves but is still working to identify the bodies, said HRW.

“Families in Tarhuna whose loved ones went missing face a difficult time moving forward with their lives,” said Hanan Salah, Human Rights Watch's senior Libya researcher. “The authorities should act on the grim discovery of mass graves by taking proper steps to identify the bodies and bringing those responsible for abuses to justice.”

In November, the U.S. Treasury sanctioned al-Kaniyat and its leader Mohamed al-Kani after finding it responsible for killing civilians whose bodies were discovered in numerous mass graves in Tarhuna, as well as torture, forced disappearances and displacement of civilians.

Salah said that not just al-Kani's militia but also senior commanders among Hifter's forces “could be criminally liable for abuses committed by al-Kaniyat militia in Tarhouna for which they had command responsibility.”

Family members of the disappeared told HRW that their relatives were not fighters but were targeted because they opposed al-Kaniyat or the 2011 uprising that led to the ouster and killing of longtime dictator Moammar Gadhafi, whose rule was supported by the al-Kani family.

Kamal al-Siwi, head of the Tripoli government's Public Authority for Search and Identification of Missing Persons, told HRW that his agency has exhumed 120 bodies, including women and children, in and around Tarhuna. Some of the bodies were found handcuffed and most were in an “advanced state of decay,” which made it hard for relatives to identify them, said al-Siwi in the HRW report.

Only three exhumed bodies have been identified so far and returned to their families for burial, added al-Siwi. He blamed the delay in identifying bodies on a lack of resources needed to operate a DNA analysis laboratory.

HRW urged foreign governments and the U.N. to help with the Libyan government's grave site investigations by providing forensic experts and conducting DNA testing.