(Bloomberg) -- The US warned Turkey against a new military campaign into Kurdish-controlled parts of Syria, saying that some recent airstrikes had posed a threat to US personnel working with Syrian partners to defeat the Islamic State. 

US Secretary of Defense Lloyd James Austin discussed the Pentagon’s “strong opposition to a new Turkish military operation in Syria,” during a telephone call with his Turkish counterpart, according to a readout released early Thursday. 

The Pentagon has said a cross-border attack by Turkey could undercut the operation by US-allied Kurdish forces against jihadists, a top priority for the US in Syria. The US has reduced its patrols with the Kurdish-led force in Syria after the group reduced its own patrols, the Defense Department said Tuesday. 

Turkish President Recep Tayyip Erdogan’s impatience to expand areas under Turkish control in Syria grew after his government blamed Syrian Kurdish fighters for a recent deadly bomb attack in Istanbul. He criticized the US and Russia for not upholding pledges to push Kurdish forces away from the Turkish border. 

Tracking the Feuds Plaguing the U.S.-Turkey Alliance: QuickTake

Turkish air strikes have been directed at Kurdish bases in Iraq and northern Syria. 

Responding to Austin, Turkish Defense Minister Hulusi Akar denied targeting coalition forces or civilians in his country’s operations, which he said were conducted in self-defense. He expressed readiness to cooperate in the battle against the Islamic State and all other terrorist organizations, according to a readout.  

Turkey sees US-allied Kurdish YPG fighters as a top threat because of their link to the separatist PKK, a Kurdish group that Turkey has been battling for decades and is considered a terrorist organization by the US and European Union. 

The PKK has denied responsibility for Istanbul bombing, although Turkish authorities said several suspects captured after the bombing in an Istanbul tourist district admitted links to the militants.

The call between the defense ministers of the two NATO allies came just hours after Turkey’s Foreign Minister Mevlut Cavusoglu criticized Washington for arming and training the Kurdish force in Syria.

“The support of some allies, primarily America, to terrorist organizations in Syria is clear and obvious, so we say that they should terminate such support,” Cavusoglu said at a presser on the sidelines of a NATO ministerial meeting in Bucharest on Wednesday. “We will determinedly maintain our struggle against these terrorists wherever they are in Iraq or Syria.”

All About the YPG, the Syrian Kurds Vexing Turkey: QuickTake

Any flare-up of tensions between Turkey and the US over Syria could deepen the mistrust on both sides of the alliance, which are yet to surmount differences over Turkey’s purchase of a Russian missile defense system at a time when Erdogan is seeking to buy dozens of American-made F-16 warplanes and upgrade kits to modernize the country’s existing fleet.

©2022 Bloomberg L.P.