Saturday marked yet another time that Russian and U.S. coalition planes entered the same battle space over Syria in the past two weeks, the Pentagon said in a press briefing Tuesday, underscoring the need for the two countries to work together to establish stricter safety protocols in the war-torn country since Russia started airstrikes there. What's even more worrisome, said Col. Steve Warren, a spokesperson for the Department of Defense, is how frequently Russian planes have diverted from their flight paths to look at U.S. drones operating over Syria in search of ISIS targets.

The incident Saturday took place at the same time U.S. and Russian defense officials were meeting about how to establish protocols for flying in Syria as fighting continues between regime forces, supported by Russia, and rebel groups, Warren said. 

"They came into visual contact of one another," Warren said. "Everyone went about their business. [But] it is dangerous without very clearly laid-out protocols.

Warren said it is not suprising that U.S. and Russian planes have come into visual contact, but what's more worrisome is the Russian jets shadowing U.S. drones.

"We have seen where the Russians are flying a pattern ... where they come over and take a quick look at the drones."

Fox News reported last week that there had been three separate instances where Russian fighter jets shadowed U.S. predator drones over ISIS-controlled Syria, including its de facto headquarters in Raqqa, as well as along the Turkish-Syrian border near Korbani.

“The first time it happened, we thought the Russians got lucky. Then it happened two more times,” one official told Fox News last week.

Warren said he expected there to be more meetings between the U.S. and Russia about what to do when their planes enter the same airspace.