Israel's defense minister on Tuesday, May 28 signaled that his military is prepared to strike shipments of advanced Russian weapons to Syria, in a rare implied threat to Moscow, AP reported.

Defense Minister Moshe Yaalon issued his warning shortly after a top Russian official said his government reserves the right to provide Syria with state-of-the-art S-300 air defense missiles.

Israel has been lobbying Moscow to drop the sale, fearing the missiles would upset the balance of power in the region and could slip into the hands of hostile groups, including the Lebanese militant Hezbollah, a close ally of the Syrian regime.

"As far as we are concerned, that is a threat," Yaalon told reporters when asked about the S300s.

"At this stage I can't say there is an escalation. The shipments have not been sent on their way yet. And I hope that they will not be sent," he said. But "if God forbid they do reach Syria, we will know what to do."

Since Syria's civil war erupted in March 2011, Israel has repeatedly voiced concerns that Syria's sophisticated arsenal, including chemical weapons, could either be transferred to Hezbollah, a bitter enemy of Israel, or fall into the hands of rebels battling Syrian President Bashar Assad. The rebels include al-Qaida-affiliated groups that Israel believes could turn their attention toward Israel if they topple Assad.

Israel has carried out several airstrikes in Syria that are believed to have destroyed weapons shipments bound for Hezbollah. Israel has not confirmed carrying out the attacks. The delivery of the Russian missiles to Syria could limit the Israeli air force's ability to act.