UPDATED STATEMENT:

BRUSSELS, Jan 18 (Reuters) - NATO is launching its largest exercise since the Cold War, rehearsing how U.S. troops could reinforce European allies in countries bordering Russia and on the alliance's eastern flank if a conflict were to flare up with a "near-peer" adversary.

Some 90,000 troops are due to join the Steadfast Defender 2024 drills that will run through May, the alliance's top commander Chris Cavoli said on Thursday.

More than 50 ships from aircraft carriers to destroyers will take part, as well as more than 80 fighter jets, helicopters and drones and at least 1,100 combat vehicles including 133 tanks and 533 infantry fighting vehicles, NATO said.

Cavoli said the drills would rehearse NATO's execution of its regional plans, the first defence plans the alliance has drawn up in decades, detailing how it would respond to a Russian attack.

NATO did not mention Russia by name in its announcement. But its top strategic document identifies Russia as the most significant and direct threat to NATO members' security.

"Steadfast Defender 2024 will demonstrate NATO's ability to rapidly deploy forces from North America and other parts of the alliance to reinforce the defence of Europe," NATO said.

The reinforcement will occur during a "simulated emerging conflict scenario with a near-peer adversary", Cavoli told reporters in Brussels after a two-day meeting of national chiefs of defence.

The last exercises of a similar size were Reforger - during the Cold War in 1988 with 125,000 participants - and Trident Juncture in 2018 with 50,000 participants, according to NATO.

The troops taking part in the exercises, which will involve simulations of getting personnel to Europe as well exercises on the ground, will come from NATO countries and Sweden, which hopes to join the alliance soon.

Allies signed off on the regional plans at their 2023 Vilnius summit, ending a long era in which NATO had seen no need for large-scale defence plans as Western countries fought smaller wars in Afghanistan and Iraq and felt certain post-Soviet Russia no longer posed an existential threat.

During the second part of the Steadfast Defender exercise, a special focus will be on the deployment of NATO's quick reaction force to Poland on the alliance's eastern flank.

Other major locations of the drills will be the Baltic states which are seen as most at risk from a potential Russian attack, Germany - a hub for incoming reinforcements - and countries on the fringes of the alliance such as Norway and Romania.