Libyan military commander Khalifa Haftar raised the prospect of a dangerous new escalation in the North African country’s war with a threat to target Turkish forces backing the internationally recognized government, prompting Ankara to warn it would retaliate.

The chief of Haftar’s air force, Saqr Al-Jaroushi, vowed to unleash the “largest aerial campaign in Libyan history” with all Turkish positions now “legitimate targets for our air force.” The comments came as the head of security in the Tripoli administration said officials received information that several Soviet-era jets had arrived in Haftar’s eastern stronghold from a Russian base in Syria.

Haftar has been stung by defeats over the past week at the hands of the Tripoli government, effectively foiling his yearlong offensive to capture the capital. The strongman’s self-styled Libyan National Army, that’s backed by Egypt, the United Arab Emirates and Russian mercenaries, was dislodged from a key airbase on Monday and is encircled in one of its few remaining bastions in the country’s west.

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Ibrahim Kalin, spokesman for President Recep Tayyip Erdogan, warned Turkey would respond to any attack in the “strongest way.” A senior Turkish official said the country’s military was well prepared to defend its sites and areas under its protection using Turkish drones and warships deployed near Tripoli.