Sen. John McCain, R-Ariz., on Thursday blasted Russia's veto of a U.N. Security Council statement condemning Syrian air attacks against civilians, saying Moscow was committed to maintaining strongman Bashar al-Assad's hold on power.

McCain called the Russian vote “very disturbing” in a statement, noting that it was the second time in under a month that Moscow had blocked Security Council efforts to condemn attacks on civilians in Syria's brutal civil war.

“Incredibly, the Russian government continues to aid the Assad regime by providing the equipment and conventional weapons that are being used to commit acts such as these against the Syrian people, including innocent civilians,” the senator said.

“Such actions clearly indicate that Russia shares responsibility for the perpetuation of violence in Syria, and is certainly not a reliable partner in efforts to peacefully resolve the Syrian conflict. Today’s vote in the Security Council is ample evidence of Russia’s commitment to maintaining President Bashar al-Assad in power,” McCain added.

Assad has waged a bloody battle against insurgent groups seeking his ouster. The fight has claimed 100,000 lives according to U.N. estimates and left hundreds of thousands displaced, with aid groups warning of a humanitarian crisis.

President Obama threatened military action against Assad in 2013 after the Syrian dictator used chemical weapons on his own people, crossing a U.S. “red line.” But after congressional opposition, Obama signed on to a Russian-brokered plan that would see international observers disarm Assad’s chemical arsenal.

Republican critics, including McCain, warn that Russian President Vladimir Putin, a close ally of Assad, outplayed Obama and bolstered the Syrian leader's grip.

Obama has vowed to ensure that Syria follows through on its promise to give up its chemical weapons, but a UN agency admitted in December that Damascus was well behind key deadlines to turn over its arsenal to international inspectors.

McCain has been a strong proponent of providing increased arms and humanitarian aid to rebel groups seeking Assad’s ouster. Those calls though have divided lawmakers, with many along with the Obama administration fearing that aid could fall into the hands of anti-Western Islamic groups.