General Herbert "Hawk" Carlisle said the activity had included Russian flights to the coast of California, and around the U.S. Pacific island of Guam.
Carlisle said the number of long-range Russian patrols around the Japanese islands and Korea had increased "drastically." He said there had also been "a lot more ship activity as well."
Speaking at Washington's Center for Strategic and International Studies think tank, Carlisle showed a slide of a U.S. F-15 fighter jet intercepting a Russian "Bear" aircraft over Guam. He used the Cold War NATO name for Russia's Tupolov Tu-95 strategic bomber.
"Certainly what's going on in Ukraine and Crimea is a challenge for us and it's a challenge for us in Asia Pacific as well as Europe," Carlisle said.
He said there had been "a significant" increase in Russian activity in the Asia Pacific "and we relate a lot of that to what's going on in the Ukraine."
"They've come with their long-range aviation out to the coast of California, they've circumnavigated Guam," he said.
"That's to demonstrate their capability to do it, it's to gather intel," Carlisle said, adding that the surveillance had included observation of military exercises involving U.S. forces in South Korea and Japan.
"There are things that are concerning with respect to how they operate and how transparent they are with other nations in the vicinity," he said.
Carlisle did not give details of the incidents and the Defense Department and the U.S. Air Force and Navy in the Pacific did not immediately respond to a request for more information.
Mike Green, senior vice president for Asia at CSIS, said the frequency of incidents was up and described them as being "evocative of the Cold War".
Russian President Vladimir Putin announced in 2007 that Russia was resuming Soviet-era sorties by its strategic bomber aircraft near NATO airspace that were suspended in 1992 after the collapse of the Soviet Union.
Putin, who made the announcement during a joint military exercise with China, said the move was necessary to guarantee Russia's safety and that other nations had not followed Moscow's example in suspending such flights.
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