Col. Ibrahim al-Sharaa, the spokesman of Benghazi's Joint Security Operation Room, said that the bodies were found on Monday in an area called Garoutha, 30 kilometres from the city centre. The ages of the dead range between 17 and 25, he said.
Since the ouster of longtime dictator Moammar Gadhafi, the government has relied on militias, many of them are Islamic extremists, to preserve order.
Last month six Egyptians diplomats and embassy staffers were abducted in retaliation for the arrest of a top Islamic militia commander in Egypt.