Russia said on Monday it would supply an S-300 surface-to-air missile system to Syria in two weeks despite strong Israeli objections, a week after Moscow accused Israel of indirectly causing the downing of a Russian military jet in Syria.
The White House said it hoped Russia would reconsider the move, which U.S. National Security Adviser John Bolton called a "significant escalation" of Syria's seven-year war.
Russian Defence Minister Sergei Shoigu said Moscow had in the past obliged Israel by refraining from providing Syria with the S-300. But last week's crash, which killed 15 Russian service members, had forced Russia to take "adequate retaliatory measures" to keep its troops safe.
"A modern S-300 air defence missile system will be transferred to the Syrian armed forces within two weeks," he said. The system will "significantly increase the Syrian army's combat capabilities," he said.
President Vladimir Putin discussed the decision by phone on Monday with Israeli Prime Minister Benjamin Netanyahu, the Kremlin said.
Russia, which fights in Syria to support the government against rebels and militants, has said Syrian anti-aircraft batteries shot the IL-20 surveillance plane down by mistake shortly after Israeli jets hit a nearby target. Moscow accused Israel of creating dangerous conditions that caused the crash.
Israel, which has carried out air strikes in Syria many times during the war, said after the incident that it would work to improve "deconfliction" of its missions with Russian forces, but would not halt them.
Israel has long lobbied Moscow not to provide the S-300 to Syria, fearing this would hinder its aerial capability to strike build-ups of Iranian and Hezbollah forces in Syria.
Israeli Prime Minister Benjamin Netanyahu told Putin on Monday that supplying advanced weapon systems to "irresponsible players" would heighten dangers in the region, according to Netanyahu's office.
"Responsibility for the unfortunate incident lies with the Syrian army, which downed the plane, and Iran, whose aggression destabilises (the region)," Netanyahu's statement said. Iranian forces are in Syria to support the government in the war.
In the phone call, Netanyahu also said he told Putin that Israel would continue to protect its security and interests. The Israeli leader also agreed with Putin on continued coordination between the two countries' armed forces.
Amos Yadlin, a former head of Israeli military intelligence, tweeted that the Russian accusation Israel was to blame for the Russian plane being shot down was "fake news...meant to assuage diplomatic pressures and cloud the responsibility of Syrian and Russian officers for downing the plane.”
"Supplying S-300 increases risk by unprofessional Syrian operators first and foremost to the Russian air force, to Israel, the United States and the coalition as well as to civil aviation," Yadlin said. "Israel has been preparing for this threat for 20 years and will know how to handle it."
Originally developed by the Soviet military, the S-300 has since been modernised and made available in several versions with different capabilities. It fires missiles from trucks and is designed to shoot down military aircraft and short- and medium-range ballistic missiles.
Alexander Khramchikhin of the Moscow-based Institute of Military and Political Analysis said the S-300 could "seriously affect Israel's ability to carry out its strikes in Syria". Dmitri Trenin, director of the Carnegie Moscow Center and a former colonel in the Russian army, said the S-300 would make Israel "more careful in the vicinity of Russian assets".
Kremlin spokesman Dmitry Peskov told reporters the decision to supply the weapons was not directed at any third country.
"Russia needs to increase safety of its military and it should be clear for everyone," he said. But he also repeated Moscow's accusations that Israel was to blame for the plane's downing: "No doubt that according to our military experts, deliberate action by Israeli pilots was the reason for the tragedy and this cannot but harm our (Russia-Israeli) ties."
Syrian President Bashar al-Assad's office said: "President Putin held Israel responsible for bringing down the plane and informed President Assad that Russia will develop Syria's air defence systems."
Bolton told reporters in New York: "There shouldn’t be any misunderstanding here ... The party responsible for the attacks in Syria and Lebanon and really the party responsible for the shooting down of the Russian plane is Iran," he said.
Bolton said a political process was needed to end Syria's war but that Russia's plans with the S-300 made that difficult.
He said U.S. troops would stay active in Syria as long as Iran was involved. "We’re not going to leave as long as Iranian troops are outside Iranian borders, and that includes Iranian proxies and militias."