What on earth is Russia doing in Syria? This question has no doubt crossed many minds in recent days, as Russia began to move substantial arms and troops into Syria. There are two possible scenarios: 1) with diplomatic ties at an all time low, and heavy sanctions already in place, Russia has decided it has nothing to lose in defying the West and backing the Assad regime militarily to the bitter end; or 2) Russia is maneuvering to give itself diplomatic leverage in any Syrian settlement by raising the stakes now. Though the latter is more likely, it’s difficult to know which scenario is accurate, further complicating already tortuous US policy towards Syria.

Over the last week, various news sources have reported an increase in Russian arms and troops flowing into Syria. On Monday, the Department of Defense confirmed that the Russians are setting up a Forward Operating Base at Latakia, including prefabricated housing and SA-22 anti-aircraft missiles. Open source researchers have found photos of Russian trucks and T‑90 tanks near Latakia, increased shipments to Russia’s Syrian base at Tartus, social media posts showing that Russian troops are headed to Syria, and even satellite photos showing massive expansion of the runways, hangers and housing at Latakia.

In short, it seems that Russia is preparing to substantially increase its military presence in Syria, ostensibly to aid the refugee crisis and fight ISIS, but practically in support of the Assad regime. This doesn’t necessarily indicate an intention to commit ground troops, but certainly raises the possibility of Russian air support for Assad. There is no way to prevent this buildup: though NATO members like Bulgaria have closed their airspace to Russian flights, Iranian and Iraqi airspace remains open.

Russian military support for the Assad regime is nothing new: Russia supplies many of the regime’s weapons, and there have long been suspicions that Russian advisors in Syria may play an active role in combat. Yet direct Russian military involvement in Syria is a major escalation. More puzzling is the fact that Russia’s behavior appears to directly contradict the summer’s diplomatic efforts, which saw the first Russian-Saudi meetings in several years and rumored diplomatic attempts by the US, Russia and the Gulf States to find a negotiated settlement for the Syrian crisis.

With the United States engaged in airstrikes against ISIS, active Russian military involvement in Syria complicates the strategic situation. To start with, it inhibits the creation of an ‘ISIS-free zone’ and makes any form of no-fly zone effectively impossible. This is hardly a loss, given the many good reasons to oppose a no-fly zone inside Syria. Russia’s military support will also prevent the Assad regime from falling any time soon. Likewise, this may be less of a negative than it initially appears. Despite the Assad regime’s brutality, its collapse would likely result in further chaos, potentially strengthening ISIS.

Unfortunately, Russian military involvement in Syria also substantially raises the stakes for all involved. Any Russian air campaign runs the risk of direct conflict between U.S. and Russian forces. With U.S. fighters engaged in daily airstrikes against ISIS, Russian air presence could result in accidental clashes. This risk is especially troubling given the current high state of tension between Russia and the U.S., and the lack of military to military channels for de-conflicting Syrian airspace.

Russia’s military buildup is a complicating factor in the ongoing Syrian strategic morass. Though it remains unclear exactly what the Kremlin hopes to achieve with its military buildup, it seems probable that the increasing Russian military involvement in Syria may in fact be intended to enhance the Kremlin’s bargaining position. Ultimately, the risks raised by Russian military intervention strengthen the case for a diplomatic solution in Syria. Unfortunately, they may make it harder to find a diplomatic solution that is palatable here in Washington.