For years, Israel was without rival in the skies over the Middle East, but with the Russian military placing an advanced anti-aircraft system — the S-400 — in Syria, that dynamic has changed and turned the once open skies into a far more difficult space to navigate, according to a senior Israeli Air Force official.

“We’re living in interesting times,” the officer told reporters Sunday night, speaking on condition of anonymity.

The Syrian civil war, which has ravaged the country over the past five years, has become something of an international free-for-all, with not only hundreds of local militias, but nations from all over the world taking part in the fighting.

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A United States-led coalition of some 17 countries has been leading a large aerial campaign against the Islamic State in Syria and Iraq. Meanwhile Russia, Iran and Hezbollah have teamed up with the Bashar Assad regime to fight the various rebel groups threatening to topple the Alawite leader.

“Syria’s the global stage, everybody’s playing there,” the senior officer said.

Mixing metaphors, the officer also compared the situation in Syria to a military “laboratory,” where the visiting armies have been testing new weaponry and tactics.

“You can check weapons systems. You can check doctrines,” the officer said.

The Russians have tried and used “everything they have” — firing ballistic missiles from Russia into Syria, sending their lone aircraft carrier into the area, flying sorties out of Iran — “and they’re not the only ones,” he said.

Approximately 400,000 people are estimated to have died since March 2011 when the war began and millions have been displaced by the fighting, though figures vary between the numerous monitoring organizations.

Russia in Syria: A ‘challenge’ for Israel

In regard to both the general situation in Syria and Israel’s attempts to operate inside it, Russian involvement has been the most significant factor in creating the current dynamic in the region, the officer said.

According to the senior air force official, since their arrival in Syria some 14 months ago, the Russians have turned the “momentum” of the fighting in favor of Assad and against the Islamic State.

Barring “dramatic changes,” that trajectory will continue, arriving at some sort of equilibrium — “but not a solution” — within the next few months, the senior officer said.

For Israel, which once enjoyed nearly unchallenged air superiority in the region, the arrival of the Russian military and its S-400 missile defense system — one of the most advanced in the world — made the situation in Syria “a challenge,” he said.

Though Israel has kept out of the Syrian civil war, the Jewish state constantly monitors the Hezbollah terrorist group and its attempts to bring weapons from Iran though Syria and into Lebanon and conducts airstrikes when necessary to prevent that materiel from reaching its destination, as Prime Minister Benjamin Netanyhu has noted.

In light of the heavy Russian presence, Israel in September 2015 set up a mechanism with Moscow — involving work groups led by the deputy chiefs of both militaries — to avoid conflicts and potentially fatal misunderstandings.

However, the officer stressed that this system was limited: Israel does not inform the Russians before conducting airstrikes in Syria, nor does Russia let the Israelis in on its plans.

Since this Russo-Israeli understanding was reached last year, Israeli officials have stressed the distinction between this particular understanding and full military cooperation.

“Cooperating is not the right term. We do not coordinate [with Russia]. It’s about deconfliction and security measures so they don’t harm us, and we don’t harm them,” the officer said Sunday.

“I think we’re doing okay,” he added.

There have been reports of apparent breaches in that mechanism.

In July, for instance, a Russian drone entered Israeli airspace, apparently by accident. After multiple failed attempts by the IAF to bring it down, the unmanned aerial vehicle returned to Syrian airspace.

And in April, Israeli media reported that the Russians had fired on Israeli jets on two occasions, though the Kremlin officially denied the incidents.