The U.S. this week intercepted a half dozen Russian planes that got too close to U.S. airspace near Alaska, while Canadian planes intercepted two Russian bombers, NORAD said Saturday.

CNN, citing a U.S. official, reported that the incidents might have been related to Ukrainian President Petro Poroshenko’s visit this week to Ottawa and Washington, D.C. After Poroshenko addressed a joint session of Congress, President Obama pledged to give Ukraine $53 million in aid but no weapons for its fight against pro-Russian separatists.

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On Wednesday night, two Alaskan-based F-22 fighter jets identified and intercepted two Russian IL-78 refueling tankers, two Russian Mig-31 fighter jets and two Russian Bear long-range bombers just west of Alaska, officials from the North American Aerospace Defense Command (NORAD) said in a statement. The Russian aircraft then flew a loop south and headed back toward Russia.

Early the next morning, two Canadian CF-18 fighter jets intercepted two Russian Bear long-range bombers over the Beaufort Sea.

“In both instances, the Russian bombers never entered sovereign airspace,” NORAD said in its statement.

NORAD is responsible for monitoring and identifying all aircraft approaching North America and toward the sovereign airspace of either the U.S. or Canada.

But officials said it’s not that rare for U.S. jets to intercept Russian planes: The U.S. has intercepted more than 50 Russian long-range bombers during the past five year in order to visually identify the aircraft.