Britain on Thursday announced sanctions on the Kaniyat militia, which is allegedly behind a spate of gruesome murders, kidnapping and torture of civilians in Libya.

London placed restrictions on the group and its leaders Mohamed al-Kani and Abdurahem al-Kani for what it said was a "reign of terror" in the town of Tarhuna, southeast of Tripoli.

Middle East and North Africa minister James Cleverly said the militia was responsible for enforced disappearances, torture and the killing of civilians.

"These new sanctions send a clear message that those responsible for serious human rights violations or breaches of international humanitarian law in Libya will face consequences," he said in a statement.

The US Treasury announced similar sanctions against the Kaniyat militia, which is loyal to eastern strongman Khalifa Haftar, in November last year.

In June 2020, Libyan government forces discovered 11 mass graves around Tarhuna, from where Haftar began an abortive offensive against the UN-recognised government.

Locals in the town in April this year told AFP the militia, commanded by six brothers, systematically not only executed their opponents but slaughtered their entire families.

"They spared no child, no woman, no old man," said one man, calling them a "criminal gang", who paraded through the town, instilling fear with a pair of leashed, roaring lions.

The Kaniyat or al-Kani militia are among an array of armed groups who filled a power vacuum in Libya after the death of veteran dictator Muammar Ghaddafi in 2011.

Some of the bodies found in Tarhuna were blindfolded with their wrists tied.

Britain unveiled its own human rights sanctions regime last year, after departing from the European Union, and has targeted individuals and entities from Russia, Saudi Arabia, Venezuela, Pakistan, Myanmar, North Korea, Belarus and Gambia.

Last month, it announced separate sanctions under a new global anti-corruption regime.