ORLANDO, Fla.  NATO aircraft had four close encounters with Russian planes in separate incidents on Feb. 10, the Air Force's top general in charge of its forces in Europe said Thursday.

Gen. Tod Wolters, commander of U.S. Air Forces in Europe and U.S. Air Forces Africa, said three of those encounters were with Russian Su-24 attack aircraft and the fourth was with an Ilyushin Il-38 maritime patrol aircraft. Speaking at the Air Force Association's Air Warfare Symposium, Wolters described the encounters as four separate incidents, and said there have not been any close contacts since then.

The trend of Russian aircraft flying dangerously close to planes flown by U.S. and other allied forces — which has raised concerns about the possibility of accidents or increased tensions between the two powers — has "plateaued" in the past six months or so, Wolters said. The Air Force continues to keep a close watch on such encounters, he added, and top officials try to talk to the Russians to get information about such encounters — sometimes fruitlessly.

"Sometimes we don't get the answer we prefer," Wolters said. "Sometimes we get no answer at all."

The four incidents "were not similar in nature," Wolters said, but NATO officials are concerned about the degree of closure and the final range at which the Russian aircraft approached the NATO planes. When asked whether he believed such close calls are caused by errors in judgment on the part of Russian pilots or expressions of policy, Wolters said he suspected it's "a little bit of both," but primarily a judgment issue.

Wolters also said that no decisions have yet been made on deploying F-35 aircraft to Europe and the Pacific, but that he's confident both theaters will receive the advanced plane soon. He suspects that when the F-35 is deployed it will likely be to RAF Lakenheath in the United Kingdom.

"The F-35 itself is a game-changing resource," Wolters said of the fighter's stealth capabilities and ability to relay information. "It delivers an effect in the battlespace that we haven't seen before. It affords us access that we haven't seen before. It serves as a powerful, powerful deterrent."