Tension gripped Misrata after the death of a rebel from the western city who was credited with capturing late Libyan leader Muammar Gaddafi, but who was later abducted and tortured in a rival town.
Omran Ben Shaaban, 22, was kidnapped by armed men in July in the oasis town of Bani Walid, which was a final bastion of Gaddafi loyalists in the 2011 conflict, his brother Walid told AFP.
Shaaban tried to escape his assailants but they caught up with him and shot him in the neck and stomach, Walid added.
The Misrata native was freed 50 days later in critical condition thanks to the mediation efforts of Mohammed Megaryef, president of the ruling General National Congress (GNC), who visited Bani Walid last week.
But he later died in a French hospital where he was sent for treatment, Walid said.
On Tuesday, a private plane flew Omar Ben Chaaban's corpse to the coastal city of Misrata where his family, friends and well-wishers were waiting.
This former rebel had shot to fame last year with several photographs and videos showing him grabbing Gaddafi at the moment of his capture on October 20, 2011 in Sirte, before he was killed.
His death puts an added strain on the already tense relationship between Misrata and Bani Walid, neighbouring but historically rival towns which found themselves on opposite sides of the 2011 conflict.
Former rebels from Misrata and other Libyan cities consider that Bani Walid was not "liberated" of the "remnants" of former regime loyalists.
"We will take revenge militarily but legitimately," said Walid Ben Shaaban who commands a brigade made up of ex-rebel fighters.
"We will give the authorities an opportunity to tackle the issue but if they fail to act, we know how to make our move," he told AFP.
Late Tuesday, the GNC, which is the highest political authority, ordered the ministries of defence and interior to find those who kidnapped Shaaban and "use force if necessary."
It also issued a statement published on the official LANA news agency lamenting the "loss of a brave hero" and vowing to take all necessary measures to bring the perpetrators to justice.