Tensions between Turkey and the United States are poised to escalate after the Turkish air force carried out a series of pre-dawn strikes against Kurdish militants in Iraq’s Sinjar region and northeastern Syria, killing foes and friends alike, with potentially disruptive effects on the war against the Islamic State.

Five peshmerga fighters attached to the Kurdistan Regional Government (KRG), Turkey’s closest regional ally, perished in the airstrikes on Mount Sinjar. At least 20 fighters from the Syrian Kurdish People’s Protection Units (YPG), the US-led coalition’s top ally in the fight against the jihadis in Syria, were killed when Turkish jets hit their headquarters in Mount Qarachok near the town of al-Malikiyah, known as Derik in Kurdish. A building housing a local radio station was also destroyed in the attack.

The strikes come at an especially critical moment, as the US-led coalition presses its offensive against IS in Raqqa.

Officials from the US-led coalition familiar with the details of the strikes said Turkish officials had informed the United States of its plans before they were executed. The officials told Al-Monitor on strict condition that they not be identified that Turkey had sought to coordinate the strikes with the Qatar-based Combined Air Operations Center (CAOC), which controls and commands the air campaigns in Syria and Iraq, among others, with US allies. According to one of the officials, “CAOC turned them down.” Turkey went ahead with the strikes anyway.