In a move that was linked to the major suicide bombing against a wedding in southern Turkey over the weekend, Turkish forces attacked ISIS targeted in and around Jarabulus today, along the Syrian border. In a move that perhaps surprised no one, Turkey’s attacks on northern Syria centered primarily not on ISIS, but on the Kurds.

While Jarabulus was hit a bit, nominally to “open a corridor” for the Islamist rebels preparing to attack the city from Turkish soil, the Turkish military also heavily bombarded Manbij, a city which last week was captured by US-backed Kurdish Syrian Democratic Forces (SDF) troops.

The attack on Manbij reflects Turkey’s long-standing warning to never allow Kurds to hold territory west of the Euphrates River. Manbij is on the western shore. Yet last week Turkish officials claimed to have been assured, by the US, that the Kurds would abandon Manbij quickly.

It remains to be seen if the US reacts to this attack. Though the US has generally looked the other way when Turkey attacked its allies in Syria, Manbij is a very recent gain, and US troops are almost certainly embedded therein, having played a role in the offensive. The US has threatened attacks on Syrian planes recently for bombing Kurdish troops just a bit further to the east, and it will be tough for them to justify looking the other way on Turkey’s attacks.