An elite Libyan unit's commander said on Monday his troops were joining paramilitaries in the eastern city of Benghazi commanded by a retired general who has vowed to eradicate "terrorism".

"We are joining the battle of 'dignity' launched by the Libyan National Army with all our men and weapons," said Colonel Wanis Abu Khamada, of the name given to the operation launched by Khalifa Haftar.

Haftar unleashed his forces, the so-called National Army, against Islamist militias in the country's second city on Friday.

Tripoli accuses him of trying to mount a coup, but Haftar has said he was responding "to the call of the people" to defend them against "terrorists".

"The battle will continue until terrorism is eradicated," added Abu Khamada, who is widely respected in Libya, especially in Benghazi.

His unit has been in many firefights with Islamist militias in the restive city.

Attacks attributed to extremist Islamists there have killed dozens of his men in recent months.

Ansar al-Sharia, a group based in Benghazi and classified as a terrorist organisation by Washington, has come in for particular blame.

In addition to Abu Khamada's men, several other officers based in the east have joined Haftar's forces, including air force personnel.