Washington, DC - Before commanding an army entrenched in Libya's civil war, Khalifa Haftar lived in the US state of Virginia with two of his sons, Khaled and Mustafa.

Lawyers say the military strongman and his sons will now have to answer to US courts, after two Libyan families last week filed a civil lawsuit accusing Haftar's forces of torturing and killing their relatives.

The lawsuit relies on a law enacted back in 1991, the Torture Victim Protection Act, which allows family members of victims of torture and extrajudicial killing to sue those responsible.

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Lawyers say most suits previously filed under the act failed to gain traction, as the majority of those accused had little or no assets in the US which would enable compensation. But Haftar and his sons are American citizens who own 17 properties in Virginia worth a total of $8m, according to the lawsuit.

"Unlike other people who engaged in torture and extrajudicial killing oversees, Khalifa Haftar and his sons are American citizens and own significant amounts of property here," said Kevin Carroll, a lawyer who represents the families.

"They can and will face American justice," Carroll said during a news conference on Monday.

The lawsuit alleges that in October 2014, forces loyal to Haftar launched an operation entitled "Operation Dignity" in the eastern Libyan city of Benghazi, during which they attacked the homes and killed six members of two families, the al-Suyids and the al-Krshinys.

Ibrahim al-Krshiny, one of the plaintiffs, "was taken into custody, stripped, bound and beaten with fists, pipes and cables," Carroll said, adding that he sustained a serious eye injury, and was beaten a second time with a broomstick and a plastic hose.

"He was forced to stand in water and be painfully electrocuted for five minutes at a time for seven and a half hours. Then he underwent what was essentially a mock execution," Carroll added.

Six brothers from the family were taken prisoner and accused of being members of the Islamic State, the suit alleges. Two were killed. Al-Krshiny was released but lost his eye.

The lawsuit accuses Haftar and his sons of using the Libyan National Army to wage "an indiscriminate war against the Libyan people" and of killing and torturing hundreds "without any judicial process whatsoever".

Libyan protesters waving flags and signs during a demonstration in the capital to demand an end to Khalifa Haftar's offensive against Tripoli [Ismail Zitouny/Reuters]

Haftar was once a lieutenant under former Libyan president Muammar Gaddafi. He defected in 1987 and moved to the US, where became a citizen and is widely believed to have worked for the CIA. He lived in northern Virginia for more than two decades.

In 2011, after Gaddafi was toppled and killed in a NATO-backed uprising, the North African country was plunged into civil war. Haftar returned to Libya where he became the chief of the self-styled LNA and his sons became military officials under his command.

Haftar and his allies have since set up an administration in the eastern part of the country that has been at war with the internationally-recognised Government of National Accord (GNA), established in a political process in 2015.

In April, Haftar, who is backed by the United Arab Emirates, Egypt and Russia, moved to capture Tripoli, Libya's capital and the seat of the UN-backed government.

UN-sponsored ceasefire talks between Libya's warring sides resumed last week after renewed violence on the ground threatened to derail the effort which aims to end the fighting. More than 1,000 people have been killed during 10 months of conflict with some 140,000 forced from their homes, according to UN figures.

A Libyan woman carries pictures of Khalifa Haftar during a demonstration to support the Libyan National Army offensive against Tripoli, in Benghazi, Libya [Esam Omran Al-Fetori/Reuters]

Experts say the conflict has left the country deeply fractured. Haftar's supporters believe he has helped restore security in Benghazi, is working to defeat Islamist groups and rebuild a stable Libya, while his opponents say he is a war criminal and an autocrat who wants to consolidate power over Libya.

"His critics believe they have found an opportunity in suing him in US courts given that he is a US citizen," said Ibrahim Hiba, a Libyan national and a teaching assistant of comparative politics and international relations at the University of North Texas.

"It is highly unlikely that Haftar intends on returning to the United States any time soon. This lawsuit, however, could put political pressure on Haftar and is a source of political and financial embarrassment as it sheds light on his sons, their properties and questions their legality."

According to the lawsuit, Haftar's sons purchased the 17 properties with cash between 2014 and 2017.

Lawyers say Haftar has not responded to the complaint, which seeks more than $75,000 in total compensation.

Fighters loyal to Libya's UN-backed government (GNA) firing weapons during a clash with forces loyal to Khalifa Haftar on the outskirts of Tripoli [File: Goran Tomasevic/Reuters]

Rights groups say armed groups and security forces loyal to the GNA and LNA have both been responsible for the deaths, injury and displacement of civilians in Libya since the conflict broke out. Thousands have also been detained, and human rights groups say torture and ill-treatment in prisons and detention centres are widespread.

"We have been advocating strongly for accountability and we have been working to come up with a framework that would enable some kind of mechanism to be put in place given the current challenges by the Libyan legal system," Ken Mayers, Chair of the North Africa Coordination Group for Amnesty told Al Jazeera.

Amnesty says impunity in Libya is "rampant" and are calling for the creation of an international investigation mechanism that would "document violations and abuses, identify those responsible for them, preserve evidence for use in future criminal proceedings, and publicly report on the human rights situation in Libya".