NATO says will begin annual nuclear drills on Monday -- but that they are not linked to the war in Ukraine.
"Steadfast Noon" is expected to see up to 60 aircraft taking part in training flights over Belgium, the North Sea and Britain to practise the use of US nuclear bombs based in Europe.
The drills -- which do not involve live bombs -- are taking place amid heightened tensions with Russia over its invasion of neighbour Ukraine.
The manoeuvres are likely to coincide with Moscow's own annual nuclear drills, dubbed "Grom", which are normally conducted in late October and in which Russia tests its nuclear-capable bombers, submarines and missiles.
NATO said the Western drills were not prompted by the latest tensions with Russia.
"The exercise, which runs until 30 October, is a routine, recurring training activity and it is not linked to any current world events," the alliance declared on its webpage, adding that no live weapons would be used.
"This exercise helps ensure that the alliance's nuclear deterrent remains safe, secure and effective," said NATO spokesperson Oana Lungescu.
Belgium is hosting the drills that will involve 14 countries and up to 60 aircraft, including the most advanced fighter jets on the market and US B-52 long-range bombers that will fly in from Minot Air Base in North Dakota, the statement said.
On Tuesday, NATO chief Jens Stoltenberg made clear that the alliance would proceed with its drills despite the tense international situation.
Cancelling the drills because of the war in Ukraine would send a "very wrong signal", he told reporters, arguing that NATO's military strength was the best way to prevent any further escalation of tensions.