In the early hours of Monday morning, two Israeli fighter jets crossed into southern Lebanon and launched a number of missiles at Syria’s strategic T4—or Tiyas—airbase in Homs province. The missiles struck a section of the base used exclusively by Iran’s Islamic Revolutionary Guard Corps (IRGC), its external specialist Quds Force and Hezbollah to house senior personnel, strategic weaponry and sophisticated drones in semi-hardened air hangars. At least 14 people were killed in the missile strike, which Russian Foreign Minister Sergey Lavrov later labeled a “very dangerous development” in an unusually harsh rebuke of the sort of Israeli action that Moscow usually has glossed over quietly.

It seems likely therefore that for the first time Israel chose not to pre-warn the Russian Ministry of Defense of its strike plans—sending a strong message about the increasing intensity of its concerns about the scale of Iran’s presence in Syria and Russia’s apparent failure to contain or limit it. Russian troops are stationed at T4 and its aircraft frequently conduct operations from its runways, making an unannounced Israeli strike even more of a bold move, and an escalatory development.

Two months ago, the world stood by and watched as Israel and Iran engaged in a brief series of intensifying tit-for-tat military engagements over the skies of Syria—in which the IRGC’s facility in T4 was again involved. In the space of several hours, an advanced Iranian drone and an Israeli F-16 fighter jet were shot down, and 12 Syrian and Iranian military facilities were damaged or destroyed.

Only a stern phone call from Russian President Vladimir Putin to Israeli Prime Minister Benjamin Netanyahu ensured that a much more expansive Israeli wave of retaliatory bombings did not take place. If it had gone ahead, the most significant Israeli-Iranian military engagement in seven years of the Syrian crisis could easily have spiraled into an uncontrollable conflict.

As President Donald Trump appears determined to bring closer the date of a U.S. withdrawal from Syria, it is not just important to remind him of the continued threat by remnants of the so-called Islamic State, but the critical importance to international security of containing and deterring Iran. There is nowhere that can be done more effectively than in Syria.

“ There is nowhere that Iran can be contained and deterred more effectively than in Syria. ”

The days of “rolling back” Iran in Syria are arguably long gone, but containment and deterrence may be all that is left to prevent what could be a debilitating Israeli-Iranian conflict fought on multiple fronts, sucking in multiple adversaries and resulting in a further destabilization of the region. This is not a challenge that can continue to be kicked further down the road and the Trump administration must urgently include it within its strategic thinking on the Syrian issue.

To all extents and purposes, the incident on Feb. 10 looked to have begun as an Iranian “bait-and-trap” operation, in which an Iranian drone (a cloned copy of an American RQ-170 Reaper captured by Iran in December 2011) was dispatched from an aircraft hangar used by Iran’s IRGC within the T4 airbase. The drone was then flown at low altitude along the Jordanian border and toward the Israeli-held Golan Heights in an attempt to lure an Israeli response.

As it crossed into Israeli airspace, the drone was promptly shot down by an Israeli AH-64 Apache helicopter and shortly thereafter, eight Israeli F-16s launched a series of strikes on the IRGC-dedicated section of T4. In what then looked like a “SAMbush,” multiple Syrian government air-defense systems activated near-simultaneously and fired a barrage of 27 surface-to-air missiles at the Israeli aircraft, bringing one down. In the two hours that followed, the Israeli Air Force launched a substantial air response that struck four IRGC and eight Syrian government targets, reportedly including the principal “command and control bunker” used to coordinate Syrian military operations nationwide.

The events of Feb. 10 were a stark reminder of the high stakes involved for both Iran and Israel in Syria. They were not and will not be the last test of an increasingly delicate relationship of mutual deterrence, which is strained further every day as Iran’s military posture in Syria continues to expand in both scope and scale. Iran has long maintained a position of influence in Syria, but since the outset of revolution in 2011, Tehran’s role and presence has exploded exponentially.

To suggest the IRGC has acquired in recent years a position of Syrian strategic depth vis-à-vis Israel would be an understatement. With at least 10 shared or dedicated military bases and more than 40 permanent military positions across the country, the IRGC commands well over 120,000 militiamen, at least 25,000 of whom are non-Syrians. As Iran and its many proxies have frequently made clear, this sizeable Syria-based force has only one long-term adversary in mind: Israel, and specifically its destruction as a nation state.

Beyond facilities and men-at-arms, Iran is now aggressively expanding from the asymmetric to the conventional, operating a fleet of sophisticated drones and an array of rockets and short-range ballistic missiles. The IRGC is also said to be ferrying in more precision missile technology—with munitions targetable to 10- to 20-meter accuracy—and constructing large-scale facilities for assembling sophisticated ballistic missiles flown into Syria directly from Iran, much like the IRGC does with Yemen’s Houthis. IRGC specialists and Hezbollah are also rumored to be cooperating with the Syrian government’s renewed research into chemical weapons—reportedly assisted by North Korean scientists—as well as new methods of delivering chemicals in short-range, tactical attacks.

“ An increasingly delicate relationship of mutual deterrence is strained further every day as Iran’s military posture in Syria continues to expand. ”

From an Israeli national security perspective, this state of affairs is totally unsustainable. However, options to reverse or to more aggressively contain this Iranian threat emanating from Syria carry great risks, including the likelihood of conflict expanding to Lebanon (where a battle-hardened Hezbollah awaits, with an arsenal of 150,000 rockets and missiles) and to Palestine (where Hamas has now fallen back into the Iranian fold). An expansion to Lebanon would be catastrophic, with Israeli former government officials making clear that hundreds of populated Lebanese villages would be immediate targets of Israel’s Air Force while Hezbollah missiles are capable of destroying whole neighborhoods in Israel.

Despite the Trump administration’s very vocal support to Israel, it is also unclear whether America is at all interested in backing Israel in dealing pre-emptively with the Iranian threat in Syria. Senior Israeli delegations have visited Washington, D.C., repeatedly, hoping to secure an American pledge of support, only to be disappointed.

The fact remains that if a conflict were to break out along the Golan, the Iranian proxy network would almost certainly capture some amount of Israeli territory, albeit that probably would be temporary. By itself, such an eventuality would catalyze a political crisis in Tel Aviv and Jerusalem. Even worse is the rocket and missile threat and the ease with which thousands of projectiles could quickly overwhelm Israel’s Iron Dome, David’s Sling and Arrow 2 and 3 defense systems, leaving the country’s small and vulnerable critical infrastructure open to attack and possible destruction by precision-guided missiles. For example, a mere 12 electricity plants provide for all of Israel’s needs, and all currently sit in range of Iran-provided missiles in Syria and Lebanon.

Israel has therefore leaned on Russia and Putin to balance or contain the extent and nature of Iran’s expanding role in Syria. Israeli officials appear convinced that Moscow has the necessary leverage to do this, and the will to do so, but the results speak to a different story. Israeli officials can explain in great detail their solid red lines that when crossed by Iran will result in deterrent military action in Syria. But red lines are not necessarily crossed in an instant, through a single bold action. If Prime Minister Benjamin Netanyahu had been told in 2011 that Iran would be in 2018 what it is today, he no doubt would have exclaimed that such a scenario was an existential red line.

And yet this is where we are today, thanks in part to Russia’s close coordination with the IRGC in propping up Bashar al-Assad. In fact, one retired senior Russian military officer told me recently that Russian Spetsnaz special operators have become “blood brothers” with their Hezbollah “comrades,” with the former describing the latter as the most capable partner force they’ve ever worked with. Moreover, the IRGC has fixed bases on some of the same facilities that Russia’s military operates out of. The T4 airbase is only one example. Another is Shayrat, where the sarin gas attack on Khan Sheikhoun was launched in April 2017. Similarly, local sources tell me Russian personnel often frequent the only two military bases solely under IRGC command, in Jabal Sharqi and al Kiswah near Damascus. Russia and Iran may have differing strategic visions for Syria’s future, but there is no sign of them ending their marriage anytime soon.

“ Russian Spetsnaz special operators have become ‘blood brothers’ with their Hezbollah ‘comrades.’ ”

After a brief lull following the events of Feb. 10, Israel’s Air Force has now resumed its air strikes on Iran-linked military targets in Syria, as pre-dawn events on Monday confirm. Meanwhile, opposition sources tell me Iranian militiamen are preparing for new offensive operations into southern Syria in the coming weeks, having massed in loyalist areas of southwestern Damascus. Syrian regime tanks and artillery systems reportedly are being deployed into Syria’s southwestern de-escalation zone. Although that zone’s ceasefire, negotiated in part by the U.S., may be largely holding, a 5- to 8-kilometer line demarcating a buffer zone along Israel’s border that is excluded to Iran-linked militias remains blurry at best. In fact, the IRGC’s Quds Force maintains several positions along the line itself and other IRGC-backed militia groups operate freely in regime-held areas nearby. This is far from a durable security solution for Israeli concerns.

The challenges posed by the Syrian crisis are many, but the Iran threat has too often been overlooked. Given the potential strategic consequences, the United States has a vital interest in tackling Iran and supporting a key ally, Israel. To do so, the Trump administration should seriously consider exploiting America’s years-old contact with vetted elements of the Free Syrian Army’s Southern Front in the southwest of the country in order to convert them into local defense forces (LDF).

This would be a continuation of the U.S. preference to work “by, with, and through” local elements in a light footprint approach that places the onus on locals to secure their and our interests simultaneously. While working diplomatically to reinforce southern Syria’s de-escalation, these forces—potentially trained, equipped and supported by Jordanian and U.S. special operations forces—could become a lynchpin of deterrence against any further Iranian expansion toward Israel or government-led offensives in the same direction. In the event of any such threatening moves, these LDFs would be positioned to respond defensively, with the full support of their state backers: Israel, the U.S., and Jordan.

The United States should also intensify intelligence sharing with Israel on Iran’s continued malign activities in Syria, taking the opportunity at the same time to highlight the scale of the threat to the general public. When presented with especially flagrant threats, the U.S. should also consider joining the Israeli Air Force in conducting punitive and deterrent strikes on IRGC targets in Syria.

Ultimately, the IRGC will understand only one language: that of force, and mainly when that force targets Iranians, not necessarily its more expendable non-Iranian proxies. There will always be a danger of counter-escalation, but Israel has proven remarkably adept at designing a carefully calculated series of responses to Iran that have—with one recent exception—prevented a spiral of escalation. However, they have not achieved anything close to containment, which is why a gradual escalation in action is necessary.

Finally, the U.S. should substantially expand its terrorist designation of IRGC and Quds Force-linked militias in Syria and the sanctioning of their leaders and those who facilitate Iran’s expansive facilitation network. While such sanctions-focused measures are far from sufficient to tackle the Iranian state and proxy threat, when paired with other more direct and kinetic actions laid out above, they should come to form a more cohesive counter package aimed at aggressively containing and deterring a threat that will soon become entirely irreversible and thus make a future conflagration inevitable.