Libya’s Government of National Accord on Saturday moved fighters closer to Sirte, a gateway to Libya’s main oil terminals, which it says it plans to recapture from the eastern-based Libyan National Army.
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, witnesses and GNA commanders told Reuters.
The GNA recently recaptured most of the territory held by the LNA in north-west Libya, ending eastern commander Field Marshal Khalifa Haftar’s 14-month campaign to take the capital, Tripoli.
The new front line was then formed 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 Russia, has threatened to send troops into Libya if the GNA and Turkish forces try to seize Sirte.
The US claimed Russia sent warplanes to Jufra through Syria to support the LNA. Moscow and the LNA deny this.
The LNA has itself sent fighters and weapons to bolster its defence of Sirte, already badly battered from earlier phases of war and chaos since the 2011 revolution against longtime autocrat Muammar Qaddafi.
The US Defence Department revealed in a report on Thursday that Turkey sent between 3,500 and 3,800 Syrian mercenaries to Libya in the first three months of this year before the Tripoli forces' successes in late May.
The publication, which is the first to outline Turkish involvement in Libya's war, said Ankara paid and offered citizenship to thousands of mercenaries fighting alongside Tripoli-based militias against Field Marshal Haftar's troops.
Military tension mounted this week after a deal to end the blockade of Libyan oil fields collapsed, depriving the country of its most important economic resource and the National Oil Corporation of more than $7 billion (Dh25.71bn) in revenue.
On Friday, the National Oil Corporation warned that international powers were pulling the country towards an escalation likely to extend to the oil and gas facilities.
A "large number" of foreign mercenaries are occupying oil installations, most recently Libya's largest port of Es Sidra, it said.
During a UN Security Council session on Libya this month, Secretary General Antonio Guterres called for a demilitarised zone to be set up around Sirte to prevent new clashes as violence escalated.
“The conflict has entered a new phase with foreign interference reaching unprecedented levels, including in the delivery of sophisticated equipment and the number of mercenaries involved in the fighting,” Mr Guterres said.
On Saturday, the leaders of France, Germany and Italy threatened for the first time to use sanctions against countries that continued to breach a UN arms embargo on Libya.