U.S. and Russia remain at odds in skies over Syria

ISTANBUL -- U.S. Defense Secretary Ash Carter on Tuesday demanded talks with Russia to keep each other's warplanes from colliding or attacking each other over Syria.

The Russians are mostly bombing rebels in the west who are fighting the Assad dictatorship. And the skies are getting very crowded.

Close calls between Russian and U.S. warplanes in Syria

Five days into its air campaign in Syria, Russia said its fighter jets targeted several ISIS positions on Tuesday.

But once again, some of the locations Russia says it hit is not in an area controlled by ISIS.

The U.S. says that what Moscow is really doing is propping up the Syrian regime by attacking its opponents, including some groups linked to al Qaeda but also moderate rebels who are backed by America.

As CBS News Pentagon correspondent David Martin reported Monday, Syrian airspace is increasingly crowded, with both the U.S. and Russia launching airstrikes in Syria -- but backing different sides in the country's civil war.

Neighboring Turkey -- a NATO member and a key U.S. ally -- accused Russian war planes of violating its airspace twice over the weekend.

Inside the U.S. headquarters controlling airstrikes against ISIS

And Tuesday, Turkey said eight of its F-16 fighter jets were harassed by an unidentified MIG-29 -- a Soviet-era fighter aircraft.

"For us, this doesn't look as an accident," said NATO Secretary General Jens Stoltenberg. "This is a serious violation of the airspace." Stoltenberg called on Russia to avoid escalating tensions.

As Russia seems to reassert itself as a superpower, its behavior is angering the U.S. and its allies.

Stoltenberg said Russia's substantial buildup of forces in Syria includes ground troops.

But a senior official in Moscow said Russian ground troops will not carry out operations inside Syria.