The sudden appearance of Russian forces in Syria in recent weeks is raising concerns about inadvertent conflicts with the U.S.-led coalition. But while much of the spotlight may be on Russian President Vladimir Putin’s bid to prop up the Assad regime and the escalating diplomatic tensions with Washington, Russia’s gambit presents a challenge for another regional country trying to enforce its own red lines: Israel.

Syria has for decades served as an important transit point and source for arms going to the Lebanese terrorist group Hezbollah. Hezbollah and its principal backer, Iran, have dispatched thousands of fighters to help bolster the Bashar al-Assad regime’s degraded army – in large part to preserve this key supply route.

Until now, Israel has conducted airstrikes inside Syria either in retaliation for cross-border fire, or to mitigate future threats by bombing weapon transfers to Hezbollah. Some of these strikes are believed to have targeted sophisticated Russian-made weapons such as Yakhont anti-ship missiles and SA-17 surface-to-air missiles. And because the nuclear deal paves the way for Tehran to begin exporting arms in five years after the international arms embargo expires, Syria’s importance as a supply line for Hezbollah will only increase.

Israel’s ability, thus far, to launch strikes into Syria at will has kept an important check on Hezbollah’s expanding arsenal. Assad’s forces have consistently failed to stop the strikes, even though they possess a range of modern Russian-made air-defense systems and a handful of still-capable MiG-29 and MiG-25 fighters. That failure is due not only to the superior quality of Israeli pilots and their aircraft, but the fatigue of Syrian personnel and their equipment after years of war.

Now, with an increased Russian presence in Syria, Jerusalem faces new obstacles. Despite an agreement between Putin and Israeli Prime Minister Benjamin Netanyahu to coordinate operations in Syria, more recent statements by Putin and Israeli Defense Minister Moshe Ya’alon indicate that Israel’s ability to strike in Syria may not have been sanctioned by the Kremlin. The deployment of certain Russian weapon systems indicate that Putin’s intentions in Syria are not limited to striking the Islamic State or combatting rebel groups hoping to bring down Assad.

The Russian force deployed to Syria appears to be small, yet still diverse and capable. It includes Su-34, Su-24, and Su-25 ground-attack aircraft as well as several attack helicopters stationed near the regime stronghold of Latakia. To protect their base from rebel attack, Russian ground troops equipped with T-90 main battle tanks have arrived in the country, along with BTR-80 armored personnel carriers and field artillery. While these tools make sense when battling an insurgency with no air force, the appearance of Su-30 fighters and SA-15 and SA-22 air defense systems does not.

The SU-30SM Flanker-C is a formidable multirole fighter that presents a challenge to most Western-developed equivalents. Highly maneuverable and capable of reaching speeds of Mach 2, Flankers in the Indian Air Force are rumored to have defeated American F-15s and Royal Air Force Typhoons in mock air engagements. Though it can conduct strikes on ground targets, evidence already suggests that their mission is intended less for targeting rebels than foreign air forces.

Last weekend, a Su-30 violated Turkish airspace, confirming Russia’s intent to use the aircraft to intimidate coalition forces. The Flankers are backed-up by the addition of Russian SA-15 and SA-22 anti-aircraft systems, which can shield against cruise missiles and low-flying fighters. Furthermore at sea, Russian warships have arrived off the Syrian coast – including the cruiser Moskva, armed with S-300 missiles. As NATO Commander General Phillip Breedlove warned last month, Russia is putting in place an effective area-denial bubble in the eastern Mediterranean.

Moscow sent a delegation to Israel last week to work out a mechanism to avoid confrontations between the two militaries – an objective that the U.S. and Russia have failed to reach in similar discussions. With no progress reported, there is even less of a chance Israel and Russia will see eye-to-eye since Jerusalem would be targeting forces with which Russia is coordinating – something the U.S.-led coalition has avoided. Indeed, Russia’s tightening alliance with the Assad regime, Iran, and Hezbollah leaves little confidence that Putin’s troops would not tip off their allies, allowing them to activate their defenses or move equipment and personnel that Israel intends to target.

If Israel chooses not to trust the Russians and instead to launch strikes into Syria without forewarning, it would have to accept the inevitable risks. Russian troops could be accidentally targeted, given their close proximity to pro-regime forces. After all, much of the equipment that Israel would be looking to prevent Hezbollah from acquiring is Russian-made and operated by Russians in Syria – including SA-22s which, according to Netanyahu, have already been transferred to the terror group. It’s also possible that Russian forces may be spooked by a sudden raid in their area, and in the fog of war, pull the trigger on Israeli aircraft.

Israeli leaders pride themselves on taking no chances with threats on their borders, and Israeli pilots have demonstrated remarkable skill in challenging circumstances. However, up against well-trained and freshly deployed Russian forces with unclear intentions, Israel may be deterred. As such, Hezbollah’s weapon supplies may continue unimpeded, which could force Israel to strike them elsewhere, adding new complexities to an already complex battlespace.

Patrick Megahan is a research analyst at Foundation for Defense of Democracies focusing on military affairs. He manages the website MilitaryEdge.org.