The North American Aerospace Defense Command intercepted two Russian and two Chinese bombers flying near Alaska Wednesday in what a US defense official said was the first time the two countries have been intercepted while operating together.

The bombers remained in international airspace in Alaska’s Air Defense Identification Zone (ADIZ) and were “not seen as a threat,” according to a statement from NORAD.

The US and Canada, which together comprise NORAD, intercepted the Russian TU-95 Bear and Chinese H-6 bombers. The aircraft did not enter US or Canadian sovereign airspace, NORAD said.

It also marks the first time H-6 bombers, which are a derivative of older Soviet bombers, have entered the Alaska ADIZ, the defense official said.

The intercept was carried out by US F-16 and F-35 fighter jets, as well as Canadian CF-18 fighter jets, according to the defense official. Support aircraft were also part of the intercept, the official said.

Russian flights into Alaska’s ADIZ are not uncommon. In May, Russia flew four aircraft into Alaska’s ADIZ, which NORAD said at the time “occurs regularly.”

But the presence of Chinese aircraft appears to be a new development. In March, the head of US Northern Command, Gen. Gregory Guillot, said China was pushing farther north into the Arctic and he expected to see aircraft there “as soon as this year potentially.”

“What I have seen is a willingness and a desire by the Chinese to act up there,” Guillot told a hearing of the Senate Armed Services Committee.  “We have seen them in the maritime. We have seen them under the cloud of a technical or scientific research, but we think it is certainly multi-mission, to include military. And then I expect to see air activity in the Alaska part of the Arctic as soon as this year, potentially.”

“It is a very big concern of mine,” he said.

China considers itself a “near-Arctic” state and has worked to expand its presence in the far north, including through its cooperation with Russia.