Marines on board USS Mount Whitney off the Norwegian coast, had gathered for a group photo on deck when the Tupolev TU-142 soared overhead.

"It's a long-range maritime patrol reconnaissance plane," said one fascinated marine after casting an expert eye over the visitor.

Although he had seen plenty of images of the aircraft, this was the first time he had seen it live, so to speak.

Russia has already made clear its displeasure at NATO's Trident Juncture exercises, the largest by the alliance since the end of the Cold War.

They warned that the two-week long exercise, which it sees as an anti-Russian show of force, would not go unanswered.

According to the Russian Ministry of Defence, two Tupolev TU-142 carried out a "planned flight" of more than 12 hours.

"All flights by the Russian fleet's maritime planes are carried out strictly in accordance with international airspace regulations," the ministry said on Saturday, according to state news agency RIA Novosti.

Several states, including Sweden, Turkey and Baltic nations, have complained about Russian airspace violations in recent years.

Last week, Moscow also announced plans to test missiles in the region.

According to Avinor, the public operator of most civil airports in Norway, Russia sent a NOTAM (Notice to Airmen) about the missile tests November 1-3 in the Norwegian Sea.

Any missile testing "will not change the plan of our exercise," NATO Secretary General Jens Stoltenberg said on Wednesday.

"We have not seen anything resembling a missile test, or even ships or aircraft in the area that would be relevant to documenting or monitoring missile testing," said Robert Aguilar, captain of the USS Mount Whitney.

- Cold War leftovers -

The Tupolev's passage appeared to be part of Russia's response.

But Colonel Garth Manger, a British Royal Marine in charge of operational duties aboard the US ship, took it in his stride.

"They're watching us and we're watching them," he said.

Like the Tupolev, the USS Mount Whitney is a holdover from the Cold War era.

The third oldest vessel in the US Navy and the flagship of the US 6th Fleet, it has seen nearly 50 years' service.

Upgraded with the latest telecommunications equipment, it served as the command vessel for Trident Juncture, which is perhaps what provoked the interest of the Tupolev.

But if the flyover sparked shouts from marines on board Mount Whitney, senior officers played down any provocation.

"We are at sea, everyone's got the right to be here. It's international waters, it's international airspace," said British Admiral Guy Robinson, second-in-command of the maritime task force.

"So clearly we monitor closely. But everything we see in this exercise is that they've been safe and professional."

Jason Bohm, commanding the US marines taking part in the exercise, was equally phlegmatic: "The largest issue we have had on this exercise has been the weather."