Israel has said it will act if Russia delivers promised anti-aircraft missiles to its ally Syria, in an apparent allusion to another air raid on the neighbouring country.
Moshe Yaalon, Israeli defence minister, issued his warning on Tuesday shortly after a senior official in Moscow said the Russian government reserved the right to provide Syria with state-of-the-art S-300 air defence missiles
"As far as we are concerned, that is a threat," Yaalon said.
"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.
"But if, by misfortune, they arrive in Syria, we will know what to do."
Yaalon's comments were made before Benjamin Netanyahu, Israel's prime minister, ordered his cabinet to stay silent on the issue, according to public radio.
Earlier this month, Israel launched air raids inside Syria targeting what sources said were arms destined for the Lebanese Shia armed group Hezbollah, whose fighters have entered the conflict alongside the Syrian army.
Tensions were further stirred after the EU decided in a meeting in Brussels on Monday to lift an embargo on supplying weapons to Syria's rebels.
Syria's government joined its ally Russia in condemning the EU decision as an "obstruction" to peace efforts, while accusing the bloc of supporting and encouraging "terrorists".
The US, however, said it supported the EU move as a show of "full support" for the rebels, despite its own refusal to provide arms it fears will end up in what it believes to be extremist hands in Syria.
The lifting of the embargo "sends a message to the Assad regime that support for the opposition is only going to increase", Patrick Ventrell, US state department spokesman, said.
Russia said the S-300 missiles it planned to deliver to Syria were part of existing contracts.
"We consider these supplies a stabilising factor," Sergei Ryabkov, deputy foreign minister, said, adding they could act as a deterrent against foreign intervention.
Syria already possesses Russian-made air defences. The S-300s would expand Syria's capabilities, allowing it to counter air raids launched from foreign airspace as well.
Russia has been the key ally of Bashar al-Assad's government, protecting it from any UN Security Council action despite the civil war there that has claimed over 94,000 lives.
Both Russia and Iran remain Syria’s main weapon suppliers.
Call to include Iran
In a related diplomatic development, Russia said on Tuesday it was imperative for Iran to join the so-called Geneva 2 peace conference on Syria.
The planned conference in the Swiss city, backed by both US and Russia, aims to bring both the Syrian government and the opposition to the table to negotiate an end to the country's 26-month conflict.
In-depth coverage of escalating violence across Syria
France has already rejected the idea of Iran taking part, while the US has responded to Russia's proposal with scepticism.
An exact date for the conference has not been set yet because of what Russia described as a lack of unity among Syria's opposition.
A week into talks among Syria’s opposition in the Turkish city of Istanbul - aimed at presenting a united front on the conference - has further exhibited their divisions.
The opposition Syrian National Coalition has yet to come up with an official position on whether it is joining the peace conference or not.
Coalition members and other dissidents say progress at the meeting has been ground to a halt by conflicting bids for influence by Saudi Arabia, which reportedly wants to water down the Muslim Brotherhood's strong role in the opposition coalition, and Qatar, which apparently wants to protect the influential group's clout.
Opposition leaders have said they will only participate in talks if Assad's departure from power tops the agenda, a demand Assad and his Russian backers have rejected.