Turkey’s airstrikes against Kurdish targets north of Aleppo have not been received well by the Syrian regime. On Thursday, the Syrian Defense Ministry accused Turkey of “flagrant aggression, which targeted innocent civilians” and warned that Turkish forays into Syria are a “dangerous development that could escalate the situation.”

The Syrians expressly threatened to shoot down Turkish aircraft: “Any attempt to once again breach Syrian airspace by Turkish war planes will be dealt with and they will be brought down by all means available.”

The UK Independent explains:

The Turkish air force struck 18 different Kurdish targets in Maarraat Umm Hawsh near Aleppo on Thursday, killing up to 200 soldiers. Ankara has significantly escalated its military presence in the Syrian civil war since August, successfully driving out Isis from the border region and attempting to curb Kurdish efforts at territorial expansion, which it sees as a threat to Turkish sovereignty.

CNN describes the Turkish strike as possibly “the biggest single attack by Turkish forces against U.S.-allied Kurds” in Syria. The Kurdish fighters were advancing on ISIS positions near Afrin, about 25 miles northwest of Aleppo, when Turkey attacked them.

“There was conflicting Information on the number of dead. Turkey said its attacks killed 160 to 200 Kurdish fighters. However, a predominantly Kurdish political party in Turkey, the HDP, said 14 people, including four civilians, were killed,” CNN reports.

According to the Turkish military, mortar rounds were fired into Turkish territory from Afrin on Thursday, and the Turks responded with howitzer fire. Al-Masdar News said the Turkish howitzers were firing on Kurdish positions, “to prepare for a ground assault on Afrin canton.”

The U.S. State Department, which officially regards the Kurds in Syria as important allies against the Islamic State, denied involvement in the Turkish airstrikes and warned Turkey that action without full coordination with the U.S.-led coalition would “only benefit” ISIS.

The Turks are keenly interested in making sure Syrian Kurds don’t benefit from the impending fall of the Islamic State’s capital in Iraq, Mosul. An op-ed at the Daily Sabah on Thursday stressed the importance of clearing Kurdish YPG forces out of Afrin in Syria before Mosul is recaptured, lest they succeed in connecting their territory in Afrin with the Kurdish stronghold of Kobani to the East.

Although the YPG is a U.S. ally, the Daily Sabah piece portrays them as terrorists and war criminals who have attacked the moderate rebels of the Free Syrian Army, because the YPG is more interested in “aggressive expansionism” than defeating ISIS. Turkish airstrikes against Kurdish targets are portrayed as a reasonable response to this territorial aggression.

“Seeking to create a safe zone in northern Syria to seal the border and prevent illegal immigration, Turkey has no choice but to eliminate the YPG threat before Daesh militants leave Mosul for Raqqa and al-Bab. At this point, the FSA forces are compelled to kick the YPG out of Afrin and Manbij,” the op-ed concludes.

Turkish Prime Minister Binali Yildirim rebuffed criticism of his country’s attacks on Kurds on Friday by saying, “What anybody says regarding our fight against terrorist organizations is irrelevant.”

Yildirim promised that Turkey would do “whatever is necessary” to ensure its own safety.

He criticized U.S. support for the Syrian Kurds as “a grave mistake,” reiterating Turkey’s position that while American sees the YPG as a crucial boots-on-the-ground ally against ISIS, Ankara regards them as allies of violent Kurdish separatists in Turkey. He claimed to have received assurances from U.S. Secretary of Defense Ash Carter that Kurdish forces would withdraw west of the Euphrates River.

“We will not wait until the blade is against our skin. We will not wait for terrorist organizations to come and attack us,” thundered Turkish President Recep Tayyip Erdogan on Wednesday, positioning Turkey as what the L.A. Times calls a “wild card” in a conflict where the deck is already packed with jokers.

Certainly, the spectacle of a NATO member bombing the valued military allies of NATO is not a welcome sight at NATO headquarters. Things could get much worse.

For the moment, as Secretary of Defense Carter’s stance indicates, the U.S. is keeping Turkey in line by giving assurances that a Kurd-free buffer zone along Turkey’s border with Syria will be maintained. Things could change rapidly after the recapture of Mosul from ISIS, and especially if the Islamic State is removed from of its Syrian capital Raqqa.

In fact, as analyst Aaron Stein of the Atlantic Council put it to the L.A. Times, ISIS has been serving as a sort of buffer to keep the Turks and Kurds from each other’s throats. “When you remove ISIS, you simply create conditions for more conflict among the anti-ISIS opposition,” he cautioned.