TRIPOLI—Former Libyan dictator Muammar Qaddafi died on Thursday after being captured by forces led by the Misrata Military Council, the council said in an e-mailed statement.

Details of his detention and death will be announced later in the day in a news conference, said the council, whose troops led the assault on Qaddafi’s hometown of Sirte and acted independently from the interim government, known as the National Transitional Council or the NTC.

Qaddafi’s death comes as the NTC struggles to unite the factions that rose up against his regime. The Misrata Military Council issued its comments as NTC officials gave their own statement in Benghazi, their base during the eighth-month conflict.

“Qaddafi has been killed at the hand of the revolutionaries,” Abdel Hafiz Ghoga, NTC vice chairman, told reporters. The Misrata Military Council said it “confirmed news that the tyrant died after being captured.”

The former leader had been in hiding since fleeing Tripoli at the end of August, issuing statements that he preferred to die a martyr. His loyalists massed in Sirte, strategically important because of its airport and harbor, and in Bani Walid.

Earlier Thursday, Misratan forces announced that they had defeated the last of Qaddafi’s loyalists in Sirte. The NTC’s control of Sirte would begin the countdown to elections for a national council within eight months.