Around 70 soldiers from the forces of powerful Libyan commander Khalifa Haftar have been sent to Russia for treatment, in one of the first overt signs of cooperation between Moscow and one of Libya's armed factions, an official and a military source said.

Opponents of Haftar, head of the self-styled Libyan National Army (LNA) based in the east of the country, worry that his engagement with Russia is an attempt to challenge the fragile UN-supported government in Tripoli, which he has shunned.

Western officials see the U.N.-backed Government of National Accord (GNA) as a way to stabilize Libya, which has been caught in fighting and rivalries among competing armed factions since the 2011 civil war that toppled veteran leader Muammar Gaddafi.

An official from Haftar's forces' committee for the wounded said the fighters had left for Russia via Egypt, but did not provide any details.

A military source confirmed the transfer of 70 patients by plane from Benina airport in Benghazi to Egypt, from where they were taken to Russia. The source said this would not be the last such operation for LNA wounded.

Haftar, whose forces have been fighting against an alliance of Islamist militants and former rebels in Benghazi for two years, enjoys close ties to Egypt and the United Arab Emirates. He has cultivated his friendship with Russia, visiting Moscow twice last year to ask for military aid.

Haftar, a one-time ally of Gaddafi who returned to join the uprising in 2011, has largely shunned attempts to shore up the UN-mediated peace deal. He accuses the government of aligning itself with some of the country's Islamist-leaning forces.