U.S. Defense Secretary Lloyd Austin on Wednesday told his Turkish counterpart of his "strong opposition" to a new Turkish military operation in Syria and voiced concern over the escalating situation in the county, the Pentagon said.

Austin, in the call, expressed condolences over a Nov. 13 attack in Istanbul, the Pentagon said.

"He also expressed concern over escalating action in northern Syria and Turkey, including recent airstrikes, some of which directly threatened the safety of U.S. personnel who are working with local partners in Syria to defeat ISIS," it said in a statement, using an acronym for the Islamic State militant group.

"Secretary Austin called for de-escalation, and shared the Department's strong opposition to a new Turkish military operation in Syria."