The civil war in Syria threatened to escalate beyond its borders this week with the confirmation that Russia will supply Bashar al-Assad’s government with advanced S-300 anti-aircraft missiles. The new weapons are said to be capable of shooting down aircraft in Israeli airspace.

On Tuesday, Israeli Defence Minister Moshe Yaalon ignored the usual policy of refusing to comment on possible action against Syria. Asked how Israel would respond to the missile transfer, he replied: “Of course this constitutes a threat to us. The shipments have not yet started and we hope they won’t. But if, God forbid, they do reach Syria, we will know how to act.”

This thinly veiled warning that Israel would respond with force to the delivery of the weapons raises the prospect of a clash between Russia and Iran on one side, and the US (and possibly EU) on the other.

Military analysts suggested that an Israeli airstrike to take out the S-300 missiles on delivery could be met with a Russian response, which might, in turn, lead to a US response.

Mr Yaalon’s warning was clearly directed at both Moscow and Damascus, making clear that Israel will know if and when missiles are shipped — and will make sure they never become operational.

The Israeli government was equally concerned by the outcome of Monday’s EU foreign ministers meeting, at which the embargo on supplying arms to the Syrian rebels was dropped at the urging of Britain and France.

Israel has spent months in intense diplomacy (including visits by Prime Minister Benjamin Netanyahu to London and Moscow) trying to prevent both the Russian missile delivery and the dropping of the arms embargo.

Although the EU decision does not necessarily mean an immediate supply of arms to the rebels, it does open the prospect of an arms race in Syria, which would impact on the entire region.

The Israelis’ real concern is that Syria and its surroundings will become a freewheeling bazaar of advanced weapons, in the same way that Libya has been since the fall of Muammar Gaddafi two years ago.

Many of the weapons plundered from Gaddafi’s arms depots have reached Sinai and Gaza on Israel’s southern border. A Syrian free-for-all would be far worse because Assad’s warehouses contain chemical weapons and ballistic missiles of a quantity and quality that Gaddafi only dreamed of.