After four years of devastating civil war with more than 240,000 dead — some from government use of chemical weapons and some from government-induced starvation — Syria's President Bashar al-Assad has admitted he has a manpower problem. In fact, he has a bigger problem than that.

Assad's Russian and Iranian sponsors know that his grip on Syria is far from secure. The Islamic State group has expanded its territory in the north, and fighting in the suburbs of Damascus could trigger a collapse of the regime if one major breakthrough occurs. Thus the Syrian government has turned to brutal bombings of civilians and other measures to try to stave off what is looking more and more inevitable.

The situation could deteriorate further, and Assad may use even more desperate methods if he can find them.

Alongside, and only partly related to the Syrian civil war, the US has moved F-16 fighter jets to Incirlik, Turkey, not far from northeastern Syria. At the same time (a countermove?) the Russians have moved MiG-31M supersonic interceptors to Syria. Where are we headed?

The air base at Incirlik would allow the US Air Force to operate much closer to Islamic State group targets in both Iraq and Syria. To get Turkey's permission, however, the Obama administration had to entertain Turkish demands for a "no-fly zone" in northern Syria. The Turks want to move thousands of Syrian refugees out of Turkey and back onto Syrian soil, and to keep Syrian aircraft from operating near Turkey.

The Russians countered the notion of restricting Syrian flights by delivering to Assad six MiG-31M aircraft in a deal previously agreed to but canceled in 2009. The superfast MiG-31M is the first Russian plane equipped with a look-down/shoot-down radar.

Its original mission was to catch and shoot down the American Mach 3+ SR-71 spy plane; the SR-71 was retired, an indication of the MiG's capability. Because of its speed and ability to operate at very high altitude, the appearance of the MiG-31 in Syria appears intended to harass the F-16s and make a no-fly zone impossible.

Since a no-fly zone is much more complicated than just having American jets in the area, it is unlikely the Turkish plan will come to fruition. And in the first of several conundrums, having the US fly out of Incirlik actually helps the Islamic State group by taking the Syrian Air Force out of the war over territory in the north that the Islamic State group holds. Yes, it switches out one enemy for another, but the US is likely to be a much more cautious, and thus less deadly, enemy to the Islamic State group.

In that sense, too, the deployment of MiGs in Syria is a conundrum for Russia, which should appreciate any American activity against the Islamic State group, even if it takes place over Syrian territory. But Russia's client, Syria, would not.

The dance of aircraft is part of the larger crosscurrent regarding the future disposition of the Syrian regime, and the difference between the American position and that of the Russians and their Iranian allies.

The US wants Assad replaced by a coalition government that could include "moderate Islamists," and retain the current borders of Syria. The US effort to find and train "moderate Islamists," however, has been an abject failure, and the war is really between radical Sunnis and the Alawite Shi'a government.

The Russians, it appears, would accept some form of partition of Syria with the Assad regime retaining limited powers in the mainly Alawite area. There would also be a Sunni entity, and perhaps enclaves for Christians and Kurds. None of this has been spelled out, however, and where the behind-the-scenes negotiations are going is a guess.

The American move into Incirlik may be an indication that US-Russian negotiations are failing. But whatever the Americans and the Russians want, the Islamic State group will have to be at least a tacit party to any Syrian settlement. And unless the Islamic State group and its affiliates are definitively on the run and under siege, there is little chance they would accept any deal. And if they do, there is even less chance they would keep a deal. That leaves both the US and Russians without a dance partner, and neither wants to dance with the Islamic State group.

What should appear to be agreed upon action against the Islamic State group by Russia and the US, albeit for different reasons, is now the conundrum of what will happen when an F-16 meets a MiG.