NATO war games in 1983 inadvertently put the world on the brink of nuclear confrontation with the Soviet Union, and US officials underestimated the seriousness of the situation, according to a newly declassified document.

The incident came during a period historians now refer to as the "war scare" at the height of the Cold War, when the Soviet Union was concerned about a sudden and decisive nuclear attack from the United States and its NATO allies.

During this time, in November 1983, NATO conducted a 10-day training exercise called Able Archer that involved NATO forces across Western Europe.

According to a top-secret intelligence review conducted in 1990 and declassified this month, the Kremlin reacted with "abnormal" military and intelligence measures.

It namely placed Soviet air forces in Germany and Poland on heightened alert and carried out extra reconnaissance flights.

But US intelligence did not take the Soviet war scare seriously enough, according to the review.

Western policymakers downplayed the moves as part of a Soviet propaganda effort. Historians later realized Moscow was genuinely worried the training exercise was a front ahead of a preemptive strike.

"In 1983, we may have inadvertently placed our relations with the Soviet Union on a hair trigger," the review by the President's Foreign Intelligence Advisory Board states.

Worryingly, it took the US intelligence community several years to attach sufficient weight to the possibility that the war scare was real.

"As a result, (President Ronald Reagan) was given assessments of Soviet attitudes and actions that underrated the risks to the United States," the report states.

Relations between NATO and the Soviet-led Warsaw Pact nations were already at a historically low ebb, with NATO deploying Pershing II nuclear-capable missiles to West Germany.

Just two months earlier, the Soviets had shot down a South Korean civilian airliner they claimed was on a spying mission.

And in March 1983, Reagan had called the Soviet Union an "evil empire." Moscow, meanwhile, accused him and his advisors of "madness," "extremism" and "criminality."

Among the many recommendations in the report, authors say the United States should review how it conducts military exercises and intelligence gathering efforts to ensure these "are carried out in a way that is responsive to indications and warning for war."

More than two decades after the collapse of the Soviet Union, relations are once again strained between the West and Russia, after Moscow annexed the Crimean Peninsula and began a bombing campaign in Syria to prop up the regime of President Bashar al-Assad.

A phrase in the report sounds eerily prescient of today's woes.

"Events are moving so fast that it would be unwise to assume that Soviet leaders will not in the future act, from misunderstanding or malevolence, in ways that puts the peace in jeopardy," the report states.

The review was declassified following a request from the National Security Archive, which is affiliated with George Washington University.