Reuters reports that on Friday, Turkey began cross-border shelling the Kurdish-majority Afrin canton in northern Syria. There are also reports of busloads of Sunni Arab guerrillas of the rebel Free Syrian Army, who had been sheltered in Turkey, being sent into Afrin.

The region is dominated by the People’s Protection Units (YPG), a leftist militia that serves as the paramilitary of the Democratic Union Party, which believes in running society through decentralized socialist cooperatives.

The Turkish attack comes after an announcement early this week by the Trump administration that it would arm and train a 30,000-man strong Kurdish force to police Syria’s borders and make sure ISIL did not reemerge. Turkey is engaged in a violent campaign in neighboring eastern Anatolia against the Kurdistan Workers Party (PKK), a separatist guerrilla group that has engaged in widespread attacks against Turkish police and army. Ankara sees the Syrian Kurds as allies of the PKK, but its members and the US government both deny that allegation.

Although Turkey calls the YPG in Afrin terrorists, it does not appear to be alleging that they have conducted any particular terrorist attack on Turkish soil. Turkey was hit several times by ISIL terrorist attacks, and the YPG has been the only effective land-based military against ISIL. So you could argue that Turkey should be grateful to the YPG for ending ISIL’s territorial state, which had plotted out the blowing up of Istanbul and other cities.

In fact, the Turkish authorities never seemed very interested in rolling up ISIL in Syria. Some of their animus against the YPG comes from its having also fought Turkey-backed Arab Muslim guerrillas of a Muslim fundamentalist bent in Syria. Turkey may be hoping by this attack on Afrin to strengthen the position of the latter in northern Syria.

A few hundred Russian military observers based in Afrin were alleged by the Turkish press to have been withdrawn, though this report was denied by Russian foreign minister Sergei Lavrov. The reports emerged after Thursday’s consultations in Moscow between Turkish chief of staff Hulusi Akar and Russian chief of staff Valery Gerasimov.

No Turkish troops are alleged to have invaded, and the shelling is artillery rather than from the air. On Friday the Syrian government had pledged to shoot down any Turkish fighter jets over Syrian territory. Although Afrin is at the moment autonomous and run by the Kurds, the Syrian government is hoping to bring the latter back under Damascus, and may be playing for a Baath-Kurdish alliance against Turkey and the remnants of the rebel guerrilla fighters.

YPG fighters based further east, in Jazira (Turkish Cezire), had been key to taking back Raqqa province from ISIL, and Kurds likely feel betrayed that the US hasn’t stood up for them more against Turkey. The US State Department basically said the Turkish move is unhelpful.

It is not clear whether the erratic Turkish president Tayyip Erdogan is grandstanding with these artillery strikes into Afrin or whether this is the beginning of an attempt by Turkey to occupy and/or ethnically cleanse the Afrin Kurdish enclave.