Undeterred by pleas and warnings from Israel, Russia made clear on Thursday that it will go ahead with its planned delivery of a highly sophisticated air-defense system to Syria’s President Bashar Assad.

Prime Minister Benjamin Netanyahu reportedly warned Russian President Vladimir Putin in an emergency face-to-face meeting on Tuesday that Moscow’s sale of the S-300 missile defense system to Assad could push the Middle East into war.

But Russia’s Foreign Minister Sergey Lavrov, evidently unmoved by the dramatic Israeli warning, declared on Thursday that while Moscow was “not signing any new deals,” it would honor existing contracts with Syria, including for the air-defense systems. “We’ve already carried out some of the deal,” Lavrov said, “and we will carry the rest of it out in full.”

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A failure to honor signed contracts, Lavrov added in a television interview, would “harm the credibility” of Russia in other arms-sales contracts.

Lavrov’s statements indicated that Netanyahu’s mission to Russia — he flew to meet Putin, immediately after his return from China, for emergency talks in the Black Sea resort of Sochi — had failed. In their talks, Netanyahu reportedly told the Russian president that the S-300 had no relevance to Assad’s civil-war battles against rebel groups, and implored Moscow not to deliver the systems, Channel 2 reported.

He said that if acquired by Assad, the S-300 — a state-of-the-art system that can intercept fighter jets and cruise missiles — “is likely to draw us into a response, and could send the region deteriorating into war,” the Channel 2 report said.

On Thursday night, in response to Lavrov’s statements, Israeli officials were quoted by Channel 2 as saying that Jerusalem preferred not to describe Netanyahu’s mission as a failure, but acknowledged that Israel’s “situation would have been far better” if Putin had agreed to cancel the delivery. An Israeli source was quoted as saying that Netanyahu had told Putin the S-300s represent a weapons system that “shatters [Israel’s] qualitative edge,” presumably since it would greatly constrain the Israeli air force’s freedom of movement above Syria and neighboring Lebanon.

The Israeli source was also quoted as saying that Israel would “firmly oppose” the transfer of S-300s to Hezbollah in Lebanon.

Twice this month, Israel carried out air attacks in the Damascus area to blow up Fateh-110 ground-to-ground missile consignments en route to Hezbollah via Syria from Iran.

Lavrov said recently that the S-300s were to help Syria defend itself against air attacks. Israel suspects that Russia will deliver to Assad six S-300 missile batteries, as well as 144 missiles, the Wall Street Journal reported last week.

At their brief joint press conference Tuesday, it was clear that Netanyahu and Putin had not reached agreement on how to grapple with the Syrian crisis.

The Russian president said that the only way to resolve the crisis was via “the soonest end to armed conflict and the beginning of political settlement.”

He added: “At this sensitive moment, it’s particularly important to avoid any action that could destabilize the situation.”

Netanyahu, however, said that the volatile situation in the Middle East requires action to improve security. “The region around us is very unstable and explosive, and therefore I am glad for the opportunity to examine together new ways to stabilize the area and bring security and stability to the area,” he said. The prime minister’s bottom line was that “Israel will do whatever it takes to defend its citizens.”

Russia has continued to ship weapons to Syria, despite the civil war there, but while it has reportedly delivered less-sophisticated air-defense systems, it refrained from providing Damascus with the S-300s, which have a range of up to 200 kilometers (125 miles), and the capability to track down and strike multiple targets simultaneously with lethal efficiency.

The weapon would mean a quantum leap in Syria’s air defense capability, including against neighboring countries.

Israel reportedly attacked suspected shipments of advanced Iranian weaponry — the Fateh-110 surface-to-surface missile — in Syria with back-to-back airstrikes this month. Israeli officials signaled there would be more attacks unless Syria refrains from trying to deliver such “game-changing” missiles to Hezbollah. Hezbollah said weapons shipments won’t cease.

On Wednesday, Israel reportedly warned Assad that further attacks were being considered, and that it would “bring down” his regime if he retaliated.

On Monday, Israeli Tourism Minister Uzi Landau accused Russia of destabilizing the Middle East by selling weapons to Assad’s regime. “Anyone who provides weaponry to terror organizations is siding with terror,” Landau said.