By Polina Nikolskaya and Gabrielle Tétrault-Farber

MOSCOW (Reuters) – Russia announced on Monday it will supply an S-300 surface-to-air missile system to Syria in two weeks against strong Israeli objections, a week after Moscow blamed Israel for indirectly causing the downing of a Russian military plane in Syria.

Last week’s crash, which killed 15 Russian service members, had forced Moscow to take “adequate retaliatory measures to increase the safety of Russian military fighting international terrorism in Syria,” Defence Minister Sergei Shoigu said on Monday in a televised address.

“A modern S-300 air defense 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.

Russia, which fights in Syria to support the government, has said Syria shot the IL-20 surveillance plane down by mistake shortly after Israeli jets hit a nearby target. Russia blamed Israel for creating dangerous conditions that caused the crash.

Israel, which has struck Syria scores of times during the seven-year war, said after the incident that it would work to improve “deconfliction” of its missions with Russian forces, but would not halt them. It has long lobbied Moscow not to provide the S-300 to Syria.

Krelmin spokesman Dmitry Peskov told journalists on a conference call that 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 crash: “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 explicitly linked the Russian decision to supply the weapons to the air crash: “President Putin held Israel responsible for bring down the plane and informed President Assad that Russia will develop Syria’s air defense systems,” the Syrian presidency said.

Shoigu said Russia will equip Syrian anti-aircraft units with Russian tracking and guidance systems in order to identify Russian aircraft.

Russia in April had hinted that it would supply the S-300 to Assad’s government despite Israeli objections.

The missile system, originally developed by the Soviet military, but since modernized and available in several versions with different capabilities, fires missiles from trucks and is designed to shoot down military aircraft and short- and medium-range ballistic missiles.

Israel says its air strikes on Syria are not a threat to Russia’s ally Assad, but that it must carry them out to halt arms shipments to Iranian-backed Lebanese group Hezbollah. It has made repeated efforts to persuade Moscow not to sell S-300s to Syria, as it fears this would hinder its aerial capability.

(Reporting by Maria Kiselyova, Gabrielle Tétrault-Farber and Polina Nikolskaya in Moscow and Ellen Francis in Beirut,; Writing by Gabrielle Tétrault-Farber and Denis Pinchuk, Editing by Robin Pomeroy and Peter Graff)