The continuing convulsions in the Syrian civil war and the dying gasps of ISIS mixed with Israeli resolve at the Golan Heights DMZ today. The results were all too predictable:

The Israeli Air Force shot down a Syrian fighter jet that traveled two kilometers into Israeli airspace on Tuesday afternoon, the military said.

“Two Patriot missiles were fired at a Syrian Sukhoi-model fighter jet,” the Israel Defense Forces said in a statement. …

“It penetrated two kilometers into Israeli airspace and was shot down,” the army said.

It’s the first time in four years that the Israelis enforced the 1974 Separation of Forces Agreement against air incursions. The previous incident in 2014 was very similar, although in that case the penetration was shorter, about 800 meters, rather than the mile-plus that the fighter intruded today before the Israelis shot it down. That 2014 incident had been the first time since the 1982 Hezbollah war that Israel had shot down a Syrian fighter jet, but Israel warned today that they aren’t kidding about unannounced incursions, especially from Syria:

“Israel has a very clear policy: No plane, and certainly not a Syrian plane, is allowed to enter our airspace” without the appropriate authorization, Israel’s former Military Intelligence chief Amos Yadlin told Army Radio on Tuesday.

“Any plane identified as an enemy plane is shot down,” he said.

The Syrians have a very similar policy, of course. They shot down an Israeli fighter jet in February of this year during a bombing raid on multiple Iranian positions. The raid itself was successful, but the Israelis are watching for reprisals. Anything that looks like an attack on their Golan Heights positions is going to get a lot of attention, and fast.

Is that what Syria was planning? Perhaps, but they were also trying to root out ISIS from a nearby position, the Associated Press reported just minutes before the shoot-down:

Syrian state media says government forces have reached the frontier with the Israeli-occupied Golan Heights after capturing territory from rebels and Islamic State militants.

Al-Ikhbariya TV on Tuesday broadcast footage from the fence demarcating the U.N. buffer zone between Syrian and Israeli forces inside the Golan Heights. …

It is the first time government forces have taken up positions along the frontier since an uprising against President Bashar Assad swept through the country in 2011. Islamic State militants later seized territory from rebels along the frontier region.

So the good news is that the Syrians have defeated ISIS, and the bad news is … that Syrians replaced them. It’s possible that the fighter incursion was simply a mistake, but it’s also possible that Syria might have been hoping to use their counter-ISIS operation as a cover to push the Israelis out of their positions. Bashar al-Assad might be thinking that having Russia and Iran on the ground in Syria gives him an opportunity to seize back the Golan, even if he’s still fighting to regain his own ground in other parts of the country.

At least, that’s what the Israelis have to think, and be prepared to stop. They sent a pretty clear message about their level of preparation today.