Israel's Defence Minister Avigdor Lieberman said Tuesday that his country would attack Russian S-300 air defence systems in Syria if they were used against Israeli targets.
His remarks came a day after the Russian newspaper Kommersant reported that Moscow could soon start to deliver S-300 systems to its ally Damascus, and cited a source as warning of "catastrophic" consequences if they were attacked.
"What's important to us is that the defensive weapons the Russians are giving Syria won't be used against us," Lieberman told the news website Ynet.
"If they're used against us, we'll act against them."
Russia and Syria signed an accord in 2010 for the S-300 system but the missiles have not been delivered because of Israeli pressure, according to Kommersant.
Russian Foreign Minister Sergei Lavrov said earlier this month that no decision had yet been taken on the S-300 missiles.
The Russians have deployed the S-300 around their own Tartus naval base on Syria's Mediterranean coast and the more advanced S-400 at their Hmeimim air base in western Syria.
"We have an open line; we really do have discourse" with the Russians, said Lieberman, noting that their systems had never been used against Israel.
"For several years we've been constantly in coordination and able to avoid friction with the Russians."
Israel and Syria are still technically at war, though the armistice line on the sector of the Golan Heights which the Jewish state seized from its Arab neighbour in 1967 was largely quiet for decades until the Syrian civil war broke out in 2011.
The Israeli side of the Golan has since seen regular spillover fire, and Israel has carried out dozens of air strikes on Syrian armed forces and their allies.
Israel says its strikes aim to stop advanced weapons deliveries to Hezbollah, a Lebanese armed group allied to the Syrian government and with which the Jewish state fought a devastating war in 2006.