Russian President Vladimir Putin isn’t one to hold back. Speaking Tuesday about the lack of cooperation and intelligence-sharing in Syria, Putin said some governments have “mush for brains,” apparently referring to the U.S., AFP reported.

"I think some of our partners simply have mush for brains. They do not have a clear understanding of what really happens in the country and what goals they are seeking to achieve," Putin said while speaking at an investment forum in Moscow.

Russia began airstrikes in Syria at the end of September, and Washington as well as European countries have been quick to criticize the Kremlin for strikes that were not hitting the Islamic State group, also known as ISIS, but were instead taking out opposition forces. Russian airstrikes have allowed ISIS to gain territory, the New York Times reported. Russia has long backed Syrian President Bashar Assad while the U.S. has called for his removal.

Putin said his government had asked the U.S. for a list of ISIS targets, but that the U.S. had declined to share information with Moscow.

"Then we thought again and asked another question: Then tell us where we should not strike. No answer too," he said. "That is not a joke. I did not make this up."

Putin questioned if it was even possible for the U.S. and Russia to work together, raising fears that the situation in Syria could turn into a Cold War-style proxy conflict between Moscow and Washington. The U.S. dropped 50 tons of ammunition to rebels Sunday.

The civil war in Syria has taken the lives of more than 200,000 people since 2011 and led to the displacement of millions. In a “60 Minutes” interview that aired Sunday, President Barack Obama acknowledged the failure of a U.S. program to train opposition forces, but said the U.S. would not change its approach in Syria.

“What we are not going to do is to try to reinsert ourselves in a military campaign inside of Syria,” Obama said.