While the initial number of people wounded in the attack was reported to be 75, local media news reports put the number of those injured at 129.
"An explosion hit inside the Sa'ad Bin-Abada mosque in Majuri district of Benghazi during Friday prayers", said Col. Milud Zwai, spokesman for the eastern-based army's special forces.
A Libyan youth inspects the interior of a mosque in Benghazi on 9 February 2018, after it was hit with a twin bomb attack.
According to a military spokesperson, explosive devices were placed in bags that were left at the mosque's entrance. They said that they were remotely detonated.
Two weeks ago, around 35 people were killed by a twin bombing at another mosque in Benghazi.
Jihadists and the forces of general Khalifa Haftar have been fighting to gain control of the city for over three years before Haftar announced that his troops has retaken it last July. "Prompt, impartial investigations should bring perpetrators to justice", the group said.
The LNA was battling extremists, including some linked to ISIS and al Qaeda, as well as other opponents until late last year in the Mediterranean port city.
Haftar, who is seen as a potential contender in national elections, launched a military offensive in the city in 2014 following a series of bombing attacks.
In the past few months there have been occasional, smaller scale bombings apparently targeting LNA allies or supporters. The country has been since split between rival governments in the east and the west, each backed by an array of militias. Security in many parts of Libya is poor.