Russia has expressed willingness to accept a U.S. proposal to fight together against the Islamic State group. The Russian Defense Ministry spokesman Major General Igor Konashenkov claimed that the Pentagon has made such a request to the Kremlin.

"The Russian Defense Ministry has responded to a request from Pentagon and swiftly considered U.S. proposals to coordinate actions to fight the Islamic State terrorist group in Syria,” Russian news agency Tass quoted Konashenkov as saying. "We just need to specify some technical details that will be discussed today by representatives of the Russian Defense Ministry and the Pentagon at the expert level."

NATO Secretary General Jens Stoltenberg claimed Tuesday that Russian planes were seen in Turkey’s airspace for a second time. He said that Russian ground troops were spotted on Syrian soil as well.

"We see the violation of the Turkish airspace becomes more important, more dangerous, because it happens in a context where we see more fighting, more Russian military presence in Syria," Stoltenberg told CNN. "In addition to that, they have deployed naval assets, a large number of naval assets close to the Syrian shores. And they continue to do so."

Turkey's President Recep Tayyip Erdogan earlier warned Russia that it would “lose a lot” if it lost a “friend like Turkey.” Russia allegedly violated Turkey’s airspace for the first time Saturday while the second violation happened Sunday.

According to Tass, Russia “launched pinpoint strikes against the Islamic State targets in Syria.” Moscow claimed that it has been conducting the operation against the terrorist group at the request of Syrian President Bashar Assad.