BELGRADE, Serbia >> U.S. Senator John McCain accused Russia today of having cooperated with Syrian government forces in a chemical weapons attack that has killed more than 80 people, including more than a dozen children.

The Republican senator said at a press conference in Belgrade that he believes “the Russians knew about chemical weapons because they were operating exactly from the same base.”

He said the U.S. launched cruise missile strikes last week against the Syrian base “in a response of a chemical attack.”

“I hope that this behavior by Syria, in what clearly is cooperation with Russia and Syria together, will never happen again,” he said.

McCain said the U.S. should take out Syria’s air force as part of stopping Syrian President Bashar Assad from repeating such attacks in the future.

“I would prevent Bashar Assad from flying from his airfields if he doesn’t renounce the use of these weapons,” the former American airman said. “The United States should first tell Russia that this kind of a war crime is unacceptable in the world today.”

He said the upcoming visit by U.S. Secretary of State Rex Tillerson to Moscow should “lead to an agreement on the part of the Russians that they will not allow Syria to ever again use chemical weapons.”

“Remember, Russians made that commitment after they (Syrian government forces) crossed the so-called red line back in 2014. I hope that this will be the first item on the agenda,” McCain said.

He also said he would “make sure that we arm and train some of those who fight against Bashar Assad.”

McCain is on a tour of the western Balkans, the war-weary European region where Russia has been vying for increased military, political and economic influence.