The threat of the US military intervention in Iraq and Syria erupting into a far wider war has increased sharply in the wake of a series of Turkish air strikes against Syrian Kurdish militia forces that are aligned with Washington.

The Turkish government of President Recep Tayyip Erdogan has reported that Turkish war planes carried out 26 strikes against 18 separate targets in northern Syria this week, killing as many as 200 fighters of the Kurdish People’s Protection Units, or YPG.

The Kurdish militia, however, said the number killed was 15, including civilians. The bombing raids, which began late Wednesday, continued throughout Thursday.

The air strikes were followed on Friday by an intense Turkish bombardment of Kurdish YPG positions in the northern Aleppo countryside. Kurdish sources reported that more than 150 rockets struck the area, which the YPG had previously taken from the Islamic State (ISIS).

Whatever the real death toll, these attacks mark a major escalation in the Turkish military intervention in Syria, begun in August with an invasion dubbed “Operation Euphrates Shield.”

The air strikes prompted an angry response from the Syrian government, which vowed to shoot down Turkish warplanes should they carry out more raids on Syrian territory. “Any attempt to once again breach Syrian airspace by Turkish warplanes will be dealt with and they will be brought down by all means available,” the Syrian army command warned in a statement Friday.

For his part, Erdogan has indicated that Turkey will continue the cross-border attacks. “We will not wait for troubles to come knocking on our door,” Erdogan declared in advance of the air strikes in Syria. “We will see to it that the threats are destroyed, resolved at their source.”

These developments have ratcheted up international tensions over the Syrian conflict to their highest level since last November, when Turkish warplanes ambushed and shot down a Russian jet carrying out operations against Al Qaeda-linked Islamist militias on the Syrian-Turkish border.

In the event that Syria were to begin shooting down Turkish planes, Ankara could invoke Article 5 of the NATO charter requiring the US and other members of NATO to come to Turkey’s defense, unleashing an international war pitting NATO against not only Syria, but also its ally Russia, the world’s second-largest nuclear power.

At the heart of these tensions lie the fractious set of allies Washington has brought into the simultaneous interventions in both Iraq and Syria. While ostensibly these various state and non-state actors are united in a common struggle to defeat ISIS, in reality they are each pursuing their own mutually antagonistic interests.

US imperialism itself is seeking to carry out regime change in Syria, employing Islamist militias as proxy forces, while utilizing the anti-ISIS campaign in neighboring Iraq to consolidate its control of bases and secure the permanent deployment of US military forces in the oil-rich country.

At the same time, Washington has recruited the assistance of the Syrian Kurdish YPG militia as the main ground force in attacking ISIS positions in Syria. This has antagonized Turkey, which has intervened in Syria on the pretext of combating ISIS, but has directed its main fire against the Kurds.

This week’s attacks are aimed at dislodging Kurdish forces west of the Euphrates River and preventing the linking up of the Kurdish cantons of Afrin in the west and Kobani in the east, which would lay the basis for the creation of a Kurdish autonomous zone along Turkey’s border. The Turkish government has expressed fear that territorial gains by the Syrian Kurdish forces will strengthen the demand of Turkey’s own repressed Kurdish population for autonomy.

In the midst of the deadly combat between Washington’s supposed allies in the struggle against ISIS, US Defense Secretary Ashton Carter flew to Ankara on Friday for talks with the Turkish government on both Syria and Iraq. Carter’s remarks in Turkey appeared aimed at smoothing over tensions with Ankara, which have deepened since the abortive July 15 military coup against Erdogan, which many in Turkey believe was supported by the US. Washington, the US defense secretary said, would “continue to stand side-by-side with our NATO ally against shared threats.”

Carter also stated that there was an agreement “in principle” to allow Turkey’s participation in the ongoing siege of Mosul in northern Iraq. “Iraq understands that Turkey, as a member of the counter-ISIL [ISIS] coalition, will play a role in counter-ISIL operations in Iraq, and, secondly, that Turkey, since it neighbors the region of Mosul, has an interest [in] the ultimate outcome in Mosul,” he said.

Erdogan has expressed Turkey’s “interest” in Mosul by invoking century-old Turkish claims of sovereignty over the area.

Carter’s claim of an agreement was countered almost immediately by the Iraqi government, which had earlier indicated that it would attack any Turkish forces attempting to advance on the city. “I am unable to comment on Carter’s statement as we are unaware of any agreement to allow Turkish troops on Iraqi soil until now,” an Iraqi government spokesman said.

This is only one of the many conflicts that are surfacing in the offensive in Iraq, which has brought the mutually hostile forces of the Iraqi army, Shia sectarian militias, the Kurdish Peshmerga, Sunni tribal forces and Turkey onto the same battlefield. The ostensible objective is to drive ISIS out of the city.

There are increasing reports, however, that this is taking place, at least in part, through a deliberate funneling of the Islamist fighters into Syria, where they can be employed in the war for regime-change against the government of Bashar al-Assad. CNN reported that fighters, together with their families, have already begun arriving in the Syrian city of Raqqa.

It appears ever more likely that “victory” in Mosul, to be achieved by reducing the city to rubble and inflicting massive casualties on its civilian population, will only set the stage for a new and even more bitter conflict between the rival forces laying claim to northern Iraq and its oil wealth.

Washington and its allies are preparing for the slaughter with repeated warnings that ISIS is using the population of Mosul as human shields, thereby advancing an alibi for the mass murder of civilians in the bombardment of the city. The kinds of crimes that are being carried out was spelled out Friday with a report from northern Iraq that an air strike killed 15 women visiting a Shia shrine near the city of Kirkuk, which was the scene Friday of a series of terror attacks by ISIS. The US and its allies are the only ones carrying out bombing raids in the vicinity.

While the media parrots the line about human shields in Mosul and ignores the atrocities being carried out in the course of the offensive there, it adopts the exact opposite attitude toward events 300 miles to the west, in Aleppo. Denunciations of Syria and its ally Russia for war crimes in connection with the intense bombardment of eastern Aleppo, which is controlled by Al Qaeda-linked militias, continued even as a suspension of air strikes went into its second day on Friday and eight corridors were set up to allow civilians to leave the besieged neighborhoods.

Exceedingly few people have taken advantage of the opportunity to leave. Those that have report that the Islamist militias have used force, including live fire, to disperse those seeking to escape, and that 14 local officials who urged residents to flee were publicly executed. These reports have evoked no expression of indignation from the Western media, nor any suggestion that Washington’s proxy forces are exploiting the civilian population as human shields.