Gen Mokhtar Farnana, speaking on a Libyan television channel, said a group led by Gen Khalifa Hifter had assigned a 60-member constituent's assembly to take over for parliament.
Farnana said Libya's current government would act on an emergency basis. He did not elaborate.
Farnana said forces loyal to Hifter carried out yesterday's attack on parliament. He also said yesterday's attack on Libya's parliament was not a coup, but "fighting by the people's choice."
"We announce to the world that the country can't be a breeding ground or an incubator for terrorism," said Farnana, who wore a military uniform and stood in front of Libya's flag.
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Yesterday's attack on parliament, in which Hifter's forces kidnapped some 20 lawmakers and officials in an assault that threatened to further splinter a country dominated by the armed groups that overthrew dictator Moammar Gadhafi three years ago.
The attack, which hospital officials said killed one person and wounded nine, came after an assault Friday by Hifter's forces on Islamist militias in the restive eastern city of Benghazi that authorities said killed 70 people.
"This parliament is what supports these extremist Islamist entities," al-Hegazi said. "The aim was to arrest these Islamist bodies who wear the cloak of politics."
The fighting spread to the capital's southern edge last night and along the highway leading to the airport.
Libya's army and police rely heavily on the country's myriad of militias, the heavily armed groups formed around ethnic identity, hometowns and religion that formed out of the rebel factions that toppled Gadhafi.