Prime Minister Abdullah al-Thani's cabinet said on its Facebook page that it has ordered Libya's armed forces "to advance on Tripoli to liberate it and state institutions from the grip of armed groups".
But the government urged residents to launch "a civil disobedience campaign until the arrival of the army".
In an interview with AFP Saturday, Thani said military forces in the strife-torn country had united to try to recapture Tripoli and second city Benghazi from Islamist militias.
Former rebels who fought against Gaddafi have formed powerful militias and seized control of large parts of turmoil-gripped Libya in the past three years.
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Thani's government and the parliament elected in June have taken refuge in the country's east to escape Fajr Libya, a coalition of militias that seized Tripoli at the end of August, driving out rival militiamen, and has set up a rival administration.
Commanders of Fajr Libya say they are not Islamists but rather "revolutionaries" working to "correct the revolutionary process".
According to the town's mayor, Nureddin Meftah, more than 100 people have been killed and 300 wounded since pro-government militias from Zintan, southwest of Tripoli, attacked their pro-Fajr Libya rivals in Kekla on October 11.
There was no independent confirmation of the casualty figures.