Russia's activity against U.S. forces in Syria is Robert Brownincreasing, and so is its unprofessional nature, making the recent uptick "qualitatively different" than in the past, says a senior defense official.

On Friday morning, Russia flew an intelligence mission over a U.S. military garrison in Syria and conducted an "unprofessional" intercept of a US MQ-9, according to the senior defense official. 

The activity comes just a week after the Pentagon accused Russian aircraft of harassing MQ-9 drones for three days in a row while the drones were conducting counter-ISIS missions. 

The official said these incidents are part of an increase in activity and unprofessional behavior from Russia that has persisted since March. Over the past three or four years, there have been periodic upticks in activity, but recently, the activity has been "qualitatively different" and more aggressive. 

Also on Friday, Russian aircraft flew for an extended period of time over the al-Tanf garrison housing U.S. forces in southern Syria. The U.S. did not have aircraft that could immediately respond because the Russian mission coincided with a "gap in coverage," the official said. But the U.S. did submit a verbal protest over the deconfliction line the U.S. has with Russia. 

No obvioussingle event has triggered the increase in activity, the official said. Rather, it appears to be part of a campaign to pressure the U.S. over time to remove the small number of forces remaining in Syria. There are about 900 U.S. forces in Syria as part of the coalition to defeat ISIS. 

The official suggested that some of the Russians in Syria are generals who failed in Ukraine, and so now, in Syria, they may be trying to prove a point. While there is no indication the Russians want to harm Americans, they've shown a willingness to harass or damage unmanned aircraft. 

During the intercepts last week, Russian aircraft dropped multiple parachute flares in front of the drones, forcing the drones to conduct evasive maneuvers, and in another instance, a Russian jet engaged its afterburner after pulling in front of the drone. 

In:
• Russia
• Drone
• Syria

Eleanor Watson

CBS News reporter covering the Pentagon.

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