Russia has delivered an S-300 surface-to-air missile system to Syria, it said Tuesday, in defiance of Israeli and U.S. concerns that the arms sale would embolden Iran and escalate the Syrian war.

Defense Minister Sergei Shoigu told President Vladimir Putin during a meeting broadcast by Rossiya 24 TV: "The work was finished a day ago," adding that the system would improve the security of Russian military personal in Syria.

Russia decided to supply the system after Moscow accused Israel of indirectly causing the downing of a Russian military jet near Syria in September.

Israel voiced regret at the death of 15 Russian air crew while saying Syrian incompetence was at fault and that it was compelled to continue taking action against suspected deployments of Iranian-backed forces across its northern border.

"We have not changed our strategic line on Iran," Israeli Education Minister Naftali Bennett, a member of Prime Minister Benjamin Netanyahu's security cabinet, said Tuesday.

"We will not allow Iran to open up a third front against us. We will take actions as required," he told Israel Radio.

In Washington, State Department spokeswoman Heather Nauert could not confirm reports that the S-300 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, but I just can't confirm it."