Forty people were killed and 70 wounded on Friday after three car bombs ripped through the eastern Libyan city of Qubbah, security officials and health officials said.
Speaker of the parliament Aguila Saleh said the bombs appeared to have been in retaliation for Egyptian air strikes on nearby Derna, an Islamist militant region.
Egypt, had on Monday, launched air strikes on suspected Islamic State targets in Derna, a day after the group released a video showing the beheading of Egyptian Christian workers.
Seven days of mourning has been declared for the victims.
Libya is in chaos, with two governments and parliaments vying for legitimacy and territory, four years after Muammar Gaddafi was toppled.
The capital Tripoli is under the control of a rival government and parliament, set up after a faction called Libya Dawn seized the city in summer, forcing Thinni to flee to the east.