Libya's internationally recognised Government of National Accord (GNA) on Saturday moved fighters closer to Sirte, a gateway to Libya's main oil terminals that the GNA says it plans to recapture from the eastern-based Libyan National Army (LNA).
Witnesses and GNA military commanders said a column of about 200 vehicles moved eastwards from Misrata along the Mediterranean coast towards the town of Tawergha, about a third of the way to Sirte.
The GNA recently recaptured most of the territory held by the LNA in northwest Libya, ending eastern commander Khalifa Haftar's 14-month campaign to take the capital, Tripoli, before the new front line solidified between Misrata and Sirte.
Backed by Turkey, the GNA has said it will recapture Sirte and an LNA airbase at Jufra.
But Egypt, which backs the LNA alongside the United Arab Emirates and Russia, has threatened to send troops into Libya if the GNA and Turkish forces try to seize Sirte.
The LNA has itself sent fighters and weapons to bolster its defence of Sirte, already badly battered from earlier phases of warfare and chaos since the 2011 revolution against longtime autocrat Muammar Gaddafi.