Two Russian bombers flew over the sea north of Scotland this week, as NATO meets to discuss supplying more military aid to Ukraine.
A pair of Tupolev Tu-160 supersonic jets flew across the neutral airspace of the Barents and Norwegian seas, passing to the north of Shetland.
The Soviet-era plane is the fastest bomber in active service and capable of deploying nuclear weapons.
The Russian Defence Ministry said in a statement on Tuesday: "Two Tu-160 strategic missile carriers conducted a 13-hour flight over the neutral waters of Barents and Norwegian seas.
"Long-Range Aviation conducts periodic flights over the neutral waters of the Arctic, North Atlantic, Black and Baltic Sea, as well as Pacific Ocean.
"All flights of Russian Aerospace Forces' aircraft are implemented in strict compliance with the international rules for use of airspace."
Here's what happened and what it means.
Why has Russia done this now?
As the country's defence ministry said, Russia does make periodic flights across neutral airspace.
However, the move has been seen as a response to the NATO summit in Brussels.
Ukraine, which is not a member of the organisation, is asking for fighter jets as they brace for a renewed Russian offensive.
The two jets which passed north of Scotland followed flights by two Tupolev Tu-95s over the Sea of Okhotsk and a mission by two fighters of the same type over the Bering Sea which separates Russia from Alaska.
Those flights close to NATO's borders have been seen by some as a warning from the Kremlin.
RAF jets periodically intercept aircraft from other nations near the UK's airspace, with two Tu-95s accompanied by two Tu-142 maritime reconnaissance and anti-submarine warfare planes escorted away from British airspace last February by planes scrambled from Lossiemouth.
No British jets were scrambled on Tuesday.
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Have there been any other developments?
Norway's intelligence service said this week that Russia has deployed ships armed with nuclear weapons in the Baltic Sea for the first time since the collapse of the Soviet Union.
The Northern Fleet includes warships and submarines, and is headquartered in Severomorsk near the borders with Finland and Norway.
The Norwegian report stated: "With weakened conventional capability, the importance of nuclear weapons for Russia has increased significantly.
"The Russian strategic and regional deterrent forces have thus become increasingly important for the Russian military power."
Why is Ukraine asking for fighter jets?
Most of Ukraine's jets are from the Soviet era, and are overmatched by more modern jets deployed by Russia.
The more modern fighters can strike targets without entering Ukrainian airspace, making air defence more difficult for Kyiv.
On Tuesday, the day Russia conducted the flight north of Scotland, defence minister Oleksii Reznikov arrived at the NATO meeting and produced a handkerchief with a drawing of a fighter jet on it.
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Why haven't NATO provided the jets?
It's feared that providing American, French and Swedish jets would escalate tensions with Russia, and be seen as NATO directly entering the war.
Ukraine is not a member of the alliance so it is not bound by treaty to defend the country from attack.
U.S President Joe Biden has blunty refused to F-16s and F-35s, with NATO instead focusing on air defences and training.
Russia has the largest stockpile of nuclear warheads in the world, and has around 1,500 which are deployed - meaning ready to launch.
Vladimir Putin warned in September last year: "I want to remind you that our country also has various means of destruction, and for separate components and more modern than those of NATO countries and when the territorial integrity of our country is threatened, to protect Russia and our people, we will certainly use all the means at our disposal."
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