It was the United States vs. Russia over Syria on Tuesday, as the United States condemned Russia for its decision to go ahead with selling S-300 advanced missile systems to Syria. At the same time, the U.S. welcomed the European Union’s decision to lift an arms embargo on Syria, enabling the possibility of arming Syrian rebels, to which Russia objects.

“As you know, support for the opposition is a track that we are pursuing even as we also work with the opposition in an effort to realize the Geneva Communique and bring about the political transition that is envisioned in it,” White House press secretary Jay Carney told reporters.

Referring to the Russian arm sales to the Syrian government, Carney said, “We have made clear in the past and made clear again our firm belief that providing arms to the Assad regime does not bring us closer to the political transition that Syria deserves. So our position on that has not changed.”

The State Department said it opposed Russian sales of anti-aircraft missile to the Syrian regime, calling it “a mistake.” Spokesman Patrick Ventrell told reporters, however, that the U.S. would continue working with Russia on reaching a negotiated sustainable political settlement in Syria.

Earlier, Moscow said its plans to deliver to Damascus the S-300 missiles – designed to intercept aircraft or other missiles like Patriots NATO has already deployed on Turkey’s border with Syria — were part of existing contracts.

“We consider these supplies a stabilizing factor,” the Russian deputy foreign minister Sergei Ryabkov said, adding they could act as a deterrence against foreign intervention.

Prime Minister Binyamin Netanyahu met Russian leader Vladimir Putin two weeks ago, in an effort to forestall the transfer of the missiles to Syria. He reportedly told Putin that the missiles could be used to threaten Israeli civilian air traffic, among other things.

In recent days, there have been reports that the transfer of the advanced systems would not be carried out.

On Monday, European Union foreign ministers agreed to lift an arms embargo in order to supply weapons to Syrian rebels.

British Foreign Secretary William Hague announced, however, that “no immediate decision” would be made on sending arms to the rebels fighting Bashar Al-Assad’s regime.

Defense Minister Moshe Yaalon said Tuesday that Israel “will know what to do” if Russia delivers highly advanced anti-aircraft missiles to Syria.

“The deliveries have not taken place – I can attest to this – and I hope they do not. But if, by some misfortune, they arrive in Syria, we will know what to do,” Yaalon said.