ROME — US Defense Secretary Ash Carter called Russia’s bombing of Syrian rebels not affiliated to the Islamic State, "tragically flawed," on Wednesday, but said he still wanted technical talks with Moscow to ensure the safety of US pilots flying over Syria.

"We believe that Russia has the wrong strategy. They continue to hit targets that are not ISIL. We believe this is a fundamental mistake," Carter said Wednesday during a visit to Rome.

"We are not prepared to cooperate in a strategy which is tragically flawed, and that is why I said the United States is not collaborating with Russia," he said.

Russia launched air raids in Syria last month claiming it would target ISIS but has allegedly hit rebels fighting President Bashar al-Assad, some of whom are backed by the US. Russia considers Assad a strategic ally, while Western powers want to see him step down.

Carter said he was pushing for basic, technical discussions with Russia on how to coordinate between Russian jets flying in Syria and US jets hitting ISIS targets.

"What we are obligated to do is to agree on professional air safety procedures to protect our air crews," he said.

Talks would cover safe flying distances and common radio frequencies for distress calls.

"What we will do is continue basic, technical discussions on professional safety procedures, for our pilots flying in Syria," Carter said. "That's it. We will keep a channel open because it is a matter of security for our pilots," he added.

But Russia had yet to respond, he said.  "We have not heard back from them. We are awaiting a formal response," he said.

That contrasted with claims made on Tuesday by Russian Deputy Defense Minister Anatoly Antonov that Russia had agreed with US proposals on flight safety.