Around 50,000 soldiers, 10,000 vehicles, 65 ships and 250 aircraft from 31 countries were taking part in Trident Juncture 18, which is aimed at training the Atlantic Alliance to defend a member state after an aggression.

The show of force comes amid recent concerns over US President Donald Trump's commitment to NATO, in particular the "Article 5" mutual defence clause which requires all member states to come to the aid of another member state.

"On Article 5 and the United States' commitment, it is rock-solid," Foggo, who is also the head of NATO's Allied Joint Force Command, told reporters in Oslo.

"That commitment is evident in our acts and our deeds."

The United States is contributing the biggest contingent to Trident Juncture, including more than 9,000 Marines and an aircraft carrier deployed in Norwegian waters for the first time since 1987.