The United States will not cooperate militarily with Russia in Syria because Moscow's strategy is "tragically flawed," Defense Secretary Ash Carter said Wednesday, in his strongest comments yet on the issue.
However, he said Washington is willing to hold technical discussions with the Russians to secure the safety of its pilots.
"We are not prepared to cooperate in a strategy which as we explained is flawed, tragically flawed, on Russia's part," Carter said during a trip to Rome, renewing U.S. accusations that Russia's strikes were not focused on ISIS militants.
Russia launched its air campaign last month saying it would target ISIS. But its planes have also hit other rebel groups opposed to Syrian President Bashar Assad, Moscow's ally. Some of these groups are backed by Washington.
"Despite what the Russians say, we have not agreed to cooperate with Russia so long as they continue to pursue a mistaken strategy and hit these targets," Carter said.
"What we will do is continue basic, technical discussions on professional safety procedures for our pilots flying [over] Syria. That is it. We will keep the channel open because it is a matter of security and safety for our pilots."
The United States has put forward various proposals, including simple safety protocols, such as maintaining a safe distance between U.S. and Russian aircraft and using common radio frequencies for distress calls, officials say, adding they would be similar to regulations found in civil aviation.
Pentagon spokesman Peter Cook said on Tuesday the United States was awaiting a formal response from Russia.
Russia's deputy defense minister, Anatoly Antonov, was quoted by the Tass news agency as saying his military agreed in principle with the U.S. proposals.