The first results were expected as early as late today from an election the authorities hope will pave a way out of the turmoil that has gripped the country since the 2011 ouster of dictator Muammar Gaddafi.
Masked men broke into the home of liberal activist Salwa Bugaighis in Benghazi, an Islamist bastion, just hours after polls closed yesterday evening in an attack that drew international condemnation.
"Mrs Bugaighis was stabbed in several parts of her body but the cause of death was a bullet wound to the head," said a spokesman for the Benghazi Medical Centre.
British Ambassador Michael Aron echoed the condemnation of the killing of Bugaighis, a lawyer and a feminist who served on the National Transitional Council, the political wing of the rebellion.
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"Devastated about horrific murder of Salwa Bugaighis. Leadinglight of # 17FebRevolution & human rights champion. Sad day for # Libya," he tweeted.
The murder was also condemned by UN chief Ban Ki-moon and by Amnesty International, which called for a swift investigation.
Seven soldiers who had been deployed to provide polling day security in Benghazi were also killed, and 53 wounded, in what security officials said was an attack on their convoy by Islamist militia.
Tensions have been raised further by an armed campaign launched by a rogue former general last month to rid the eastern city of Islamists, which has drawn many regular army units to his side.
There was polling day violence in western Libya too, with gunmen seizing ballot boxes from five polling stations in Al-Jemil, forcing voting in the town to be abandoned.
There was no election either in the eastern city of Derna -- a jihadist stronghold -- or in swathes of the southern Kufra region.