Russian Defense Minister Sergei Shoigu announced Tuesday that the delivery of S-300 air defense systems to Syria has been completed.
Shoigu said Russia had delivered four S-300 launchers along with radars and support vehicles to the Syrian military, and said it would take three months to train Syrian personnel in how to operate the system.
The move followed the Sept. 17 incident in which Syrian air defenses trying to counter an Israeli strike downed a Russian reconnaissance plane over Latakia, and has sparked concerns in both Israel and the United States.
Jerusalem and Washington both contend that giving Syria S-300 surface-to-air missiles will embolden Iran and escalate the Syrian civil war.
Shoigu insisted Tuesday that the S-300s would improve the security of Russian military personnel in Syria.
Israel expressed regret at the deaths of 15 Russian crewmen in the incident, but said the Syrian forces' incompetence was at fault and that Israel is compelled to continue taking action against suspected deployments of Iranian-backed forces across its northern border.
The Kremlin has rejected the Israeli Air Force's findings on the incident, saying the Russian plane was shot down because of the presence of Israeli fighter jets in Syrian airspace.
Prime Minister Benjamin Netanyahu has vowed to continue the close security coordination between the IDF and Russian forces in Syria, carried out via a designated deconfliction channel.
In Washington, State Department spokeswoman Heather Nauert could not confirm reports that the S-300 missiles had been delivered.
"I cannot confirm that that is accurate. I hope that they did not," she told a press briefing. "That would be, I think, sort of a serious escalation in concerns and issues going on in Syria."
A senior Israeli official said Sunday that Syria's possession of the S-300 posed a "complex challenge" and that Israel was working on ways to prevent this from becoming a major threat to the country's security.
"We are dealing with the [decision] in different ways, not necessarily by preventing shipments of the air defense system," he told local media.
He said he believed that Russian President Vladimir Putin "understands that the Middle East playing field is very large," and indicated that Israel reserves the right to protect itself and that it has the support of the United States.
Also on Tuesday, the U.S. envoy to NATO said Russia must halt its covert development of a banned cruise missile system or the United States would seek to destroy it before it becomes operational.
The United States believes Russia is developing a ground-launched system in breach of a Cold War treaty that could allow Russia to launch a nuclear strike on Europe at short notice, but Moscow has consistently denied any such violation.
U.S. Ambassador to NATO Kay Bailey Hutchison said Washington remains committed to a diplomatic solution but is prepared to consider a military strike if the development of the medium-range system continues.
"At that point, we would be looking at the capability to take out a [Russian] missile that could hit any of our countries," Hutchison said.
"Countermeasures [by the United States] would be to take out the missiles that are in development by Russia in violation of the treaty. They are on notice."
She later clarified in a tweet that she was not talking about a pre-emptive strike against Russia.
"My point: Russia needs to return to INF Treaty compliance or we will need to match its capabilities to protect U.S. and NATO interests. The current situation, with Russia in blatant violation, is untenable."
In Washington, Nauert said the United States had for some time argued that Moscow was not in compliance with the treaty.
"What Ambassador Hutchison was talking about was improving overall defense and deterrence posture. The United States is committed to upholding its arms control obligations and expects Russia to do the very same thing," she said, adding that the U.S. was discussing the issue with its allies.
The Russian Foreign Ministry said such statements are dangerous and that it would provide detailed answers to Washington.
"It seems that people who make such statements do not realize the level of their responsibility and the danger of aggressive rhetoric," TASS news agency quoted spokeswoman Maria Zakharova as saying.
