U.S. aircraft diverted to avoid Russian fighter in Syria

Washington (CNN) -The U.S. military diverted two aircraft over Syria to ensure they could maintain a safe flying distance from a Russian fighter aircraft in the same area, according to Captain Jeff Davis, Pentagon spokesman.

It was the first time the U.S. needed to do so since Russia began military operations in Syria at the end of last month.

The two planes were F-16s that had departed from Turkey's Incirlik air base and were on their way to a location near the ISIS stronghold of Raqqa, a senior defense official told CNN. The U.S. aircraft that diverted were not able to complete their mission, the official said.

Since the Russians began operating in Syrian airspace, U.S. pilots have been under orders to change their flight path if there is a Russian plane within 20 nautical miles, according to the official.

Davis said the incident happened in the last few days but offered few additional details.

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"We are taking action to ensure" the planes don't come too close to each other, he said, indicating there had only been one incident so far. There is no sign the two aircraft communicated with each other.

In the recent incident, the Russian plane came within the 20 nautical mile interval. The new U.S. rules were instituted specifically because there is no agreement with the Russians yet on maintaining mutual flight safety rules and practices. In fact, the incident happened in the days after the first round of technical talks with Russia on that issue.

Without that agreement, the official said, U.S. pilots cannot count on the Russians to fly under standard safety procedures.

The official emphasized the reason for the new rules is concern about keeping American pilots safe, given the long history of aggressive Russian military intercepts against U.S. aircraft.

Russia has maintained that its operations are largely aimed at taking out ISIS and other terrorist groups, the target of U.S. operations as well. But American officials have suggested that the Russian activities seem much more in keeping with supporting Syrian President Bashar al-Assad, a close Moscow ally. The U.S. has called for him to leave power and is backing elements of the moderate opposition.

State Department spokesman John Kirby said Wednesday that "greater than 90% of the strikes that we've seen" Russia take have not been against ISIS or al-Qaida affiliated terrorists.

"They've been largely against opposition groups -- groups that want a better future for Syria and don't want to see the Assad regime stay in power," he said.