Turkish air strikes in northern Syria threatened the safety of US military personnel and the escalating situation jeopardised years of progress against Islamic State militants, the Pentagon said on Wednesday.
The public comments represent the strongest condemnation by the United States of NATO-ally Turkey's air operations in recent days against a Kurdish militia in northern Syria to date.
"Recent air strikes in Syria directly threatened the safety of US personnel who are working in Syria with local partners to defeat ISIS and maintain custody of more than ten thousand ISIS detainees," the Pentagon's spokesman, Air Force Brigadier General Pat Ryder, said in a statement.
Ryder said the escalating situation threatened the progress made in the fight against Islamic State militants in the region.
He added that the United States recognises Turkey's "legitimate security concerns."
"Immediate de-escalation is necessary in order to maintain focus on the defeat-ISIS mission and ensure the safety and security of personnel on the ground committed to the defeat-ISIS mission," Ryder added.
The United States has roughly 900 soldiers in Syria, mainly in the northeast of the country, who work with the Syrian Democratic Forces (SDF), which is led by Kurdish fighters from the YPG, to fight against Islamic State remnants.
President Tayyip Erdogan said on Wednesday that Turkey's air operations were only the beginning and it would launch a land operation when convenient after an escalation in retaliatory strikes.
Ankara launched air operations at the weekend in retaliation for an Istanbul bomb attack a week earlier that killed six people, and which it blamed on the YPG. Nobody has claimed responsibility and the PKK and YPG have denied involvement.
Turkey has previously launched military incursions in Syria against the Kurdish YPG militia, regarding it as a wing of the outlawed Kurdistan Workers Party (PKK), which Turkey, the United States and the European Union designate as a terrorist group.
This is not the first time Turkey's operations in northern Syria have threatened US personnel. In 2019, American troops in the area came under artillery fire from Turkish positions as Turkey waged an offensive against US-allied Kurdish militia at the time.