Russia, a firm ally of President Bashar al-Assad, has vehemently opposed Western intervention against the Syrian regime. That position has put a diplomatic wedge between the Russia and the U.S., one that could widen as the West considers air strikes against Assad in retaliation for an apparent chemical weapons attack outside of Damascus.

Washington and its allies blame Assad for the incident, vowing to take action in response. Assad’s regime has denied responsibility, accusing rebels of using the deadly chemicals as a tactic to provoke foreign intervention. Russia officials have stood by that narrative, pinning the chemical attack on rebels and saying a Western military strike would be a “tragic mistake.”

To better understand Russia’s position we spoke to Petr Topychkanov, an analyst with the Carnegie Moscow Center. He weighs in on how the Kremlin might react to a U.S. strike on its Syrian allies.

Syria Deeply: What would be the most likely Russian response to a Western-led air strike on Syria?

Petr Topychkanov: First of all, Russia doesn’t seem to be ready to play an active military role in Syria, because it would mean direct confrontation with the U.S. Russia doesn’t have such intentions or capabilities. So Russian reaction to a U.S. strike would depend on the legal and organizational framework of this strike. For example, Russia could agree with the participation of the U.S. in military operations under auspices of the U.N. Security Council [UNSC]. It’s more probable if the UNSC will obtain solid evidence about the use of chemical weapons by the Assad regime.

But if there is not such evidence and the U.S. decides to act without any approval from the UNSC, of course Russia would strongly criticize military action from the U.S. and its allies, and would militarily support Syria. Russia would continue to supply arms and military equipment to the Assad regime, and Russia would develop close relations with the regime in Iran to help that regime to support and provide military help to Assad.

Russia will continue to support Assad only if there is no evidence that he used chemical weapons. It would be impossible to help Assad if he did. So this is the key issue.

In case of a non-U.N. sanctioned military attack by the U.S. in Syria, Russia will review all aspects of our relations with the U.S. In that case Russia would stop cooperation in Afghanistan, and it would be a serious challenge for the United States, because a northern route is an important part of the supply chain there. There is only one way to avoid direct confrontation in Syria between Russia and the U.S., and that is to act under the UNSC.

So I think that thorough investigation of chemical weapons use is in the interest of both the U.S. and Russia.

SD: Is there anything that would stop Moscow from supporting Assad?

PT: Russia supported an idea of deep investigation and avoided direct accusations, but I think now Moscow needs very solid, strong evidence of links between this use of chemical weapons and actors in Syria to change its position. Before this, Russia didn’t receive any strong evidence about chemical weapons used in Syria, and that’s why it’s supported Assad. But if Russia gets strong evidence that it’s due to Assad, it will view it as a crime and it will change Moscow’s view.

SD: Has the international pressure on Moscow increased since last week’s attack?

PT: Do we have unity in the international community on Syria? This is the problem. That is why we cannot achieve progress in international debates about Syria, because we don’t have agreement between key actors in this field. The key actors aren’t only Russia and the U.S. and the European Union, but also the Arab states, Iran, China and even in the Security Council we don’t have a consensus on Syria. This is the problem.