Russian troops are poised near Ukraine’s borders and U.S. officials warn that an invasion could come any day. But an information war between Moscow and the West has been under way for months.

In a break with past practices, the U.S. and British governments have repeatedly stated they have secret intelligence warning that Russia is preparing to invade Ukraine. The aim, Western officials say, is to stop any such attack taking place and put the Kremlin off-balance.

U.S....

Russian troops are poised near Ukraine’s borders and U.S. officials warn that an invasion could come any day. But an information war between Moscow and the West has been under way for months.

In a break with past practices, the U.S. and British governments have repeatedly stated they have secret intelligence warning that Russia is preparing to invade Ukraine. The aim, Western officials say, is to stop any such attack taking place and put the Kremlin off-balance.

U.S. officials last week said that Russia would release a staged video depicting attacks by Ukrainian forces to justify a military invasion.

In late January, the U.K. government said it had intelligence, some of which came from the U.S., showing that Russia intended to replace the Ukrainian President with a pro-Kremlin leader.

Last year, the U.S. released a declassified document that said Russia was massing tens of thousands of troops on the Ukrainian border. At the weekend, the U.S. said a Russian attack was imminent.

Russian President Vladimir Putin has been accused by the U.S. of using disinformation ahead of previous military forays.

Photo: thibault camus/pool/Shutterstock

A senior U.S. official said the Biden administration has been engaged in a deliberate effort to share additional intelligence on Russia’s actions in Ukraine with allies and partners since the fall. Declassifying some of the information completely for public release is an outgrowth of that effort.

“We’ve seen [Russia] run false-flag operations and use the confusion to launch military action many times in recent history,” the official said of the strategy. “Exposing these plots makes it that much harder for Russia to execute them.”

The Kremlin has repeatedly denied it is planning to invade Ukraine and called the information propaganda.

“They are so consistent in their statements, saying it’s imminent, Russia will have to pay the price. Sometimes it looks as if they would prefer to see this attack,” said Russian presidential spokesman Dmitry Peskov.

Releasing information to damage or deter an enemy is an ancient tactic. What is new here is the scale of it, said Jonathan Eyal, an associate director at the Royal United Services Institute, a British defense think tank. By flagging operations early, it stops Russia’s President Vladimir Putin “resorting to the same old techniques” that Moscow used to justify incursions into Crimea in 2014 and Georgia in 2008, he said.

It is also aimed at causing confusion in Russian intelligence agencies as they search for the source of the leaks, officials said.

The U.S. in 1962 released photographs like this one showing Soviet missile deployments in Cuba.

Photo: Photo12/Universal Images Group/Getty Images

The moves aren’t without risk for U.S. and U.K. intelligence agencies. They potentially expose sources in Russia. Furthermore, if war doesn’t materialize, the U.S. and U.K. governments, which have provided little evidence for their claims, could be accused of scaremongering. It could also have no effect at all.

“So far has it deterred Putin from doing the operation? No. Has it deterred him from contemplating the use of force? No,” said Mr. Eyal.

The releases also reflect an awkward truth for Western allies: if Russian tanks roll into Ukraine, their scope for action is limited.

Both the U.S. and U.K. say they won’t send troops to Ukraine, which isn’t a member of the North Atlantic Treaty Organization. Instead, both countries have promised punitive sanctions against Moscow.

“In this case, the administration does not have a lot of arrows in the quiver. It’s probably a good idea,” said John Sipher, a retired Central Intelligence Agency officer who served in Moscow and ran the CIA’s Russia operations.

Much of the information released so far is low grade or potentially available through numerous sources, analysts said, meaning it is unlikely to compromise Western informers. The aim is for U.S. and U.K. governments to validate the information’s authenticity and give it legitimacy, security officials said.

During the Cold War, judicious publication of intelligence was used to counter Russian action. In 1962, President John F. Kennedy’s government famously released photographs of Soviet ballistic missiles in Cuba amid escalating tensions with the Kremlin.

But the tactic backfired in 2003, when President George W. Bush’s administration publicized intelligence it said showed Iraqi President Saddam Hussein’s weapons of mass destruction programs and ties to terrorist groups. Both allegations proved false.

However, in the last two decades, Mr. Putin has repeatedly exploited hesitancy by Western governments to pre-emptively enter into an information war.

The U.S., NATO and Russia are caught in a diplomatic standoff over Moscow's buildup of troops at the border with Ukraine. WSJ looks at what Russia wants and how Ukraine and its allies are preparing for a potential crisis. Photo: Andriy Dubchak/Associated Press The Wall Street Journal Interactive Edition

The U.S. accused Moscow of using disinformation before Russian forces entered Georgia in 2008 and ahead of annexing the Crimean peninsula from Ukraine in 2014. It has also accused Russia of providing support for a separatist, pro-Russian insurgency in the Donbas region of eastern Ukraine.

A turning point came with the attempted murder of Sergei Skripal in England in 2018. The former colonel in Russian military intelligence, also know as the GRU, who had lived in Britain since a 2010 spy exchange, was left critically ill along with his daughter after a nerve agent was smeared on the front-door handle of his home. Although the Kremlin denied involvement in the poisoning, the British government named and charged three men it said worked for the GRU with attempted murder.

The disclosures led to the largest expulsion of Russian diplomats from Western countries since the end of the Cold War. The aim, security officials said, was to show Mr. Putin that an attack on a sovereign state would come at a high price while aggressively fighting back on misinformation.

Last year the Biden administration moved quickly to call out Russian action toward Ukraine and has coordinated with other nations’ intelligence agencies. It warned that Russian troops were massing along Ukraine’s border. That may have cost Mr. Putin the element of surprise, said Mr. Eyal, as at the time his forces weren’t fully in place and couldn’t launch a full-scale attack. In mid-January, the U.S. said Russia had sent saboteurs into eastern Ukraine to prepare a provocation. It also published fact sheets on Russian disinformation regarding Ukraine.

U.S. State Department spokesman Ned Price has defended the credibility of Western intelligence material on Ukraine.

Photo: Andrew Harnik/PRESS POOL

The U.K. foreign office in January took the unusual step of outlining an alleged plan by Moscow to install a pro-Russian leader in Kyiv. That claim was based on an analysis of intelligence coming from several nations, including the U.S., according to a U.K. official familiar with the matter. The Kremlin called the allegation disinformation.

This novel approach has so far been accepted by the U.S. and U.K. media, who have published the governments’ allegations.

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“If you doubt the credibility of the U.S. government, of the British government, of other governments and want to, you know, find solace in information that the Russians are putting out, that is for you to do,” said State Department spokesman Ned Price when he was repeatedly pressed by a reporter that the U.S. charges lacked solid evidence.

A U.S. intelligence official said the Russia-Ukraine material that has been released so far went through standard declassification channels, rather than some special task force to handle it.

“The Intelligence Community leveraged its established process that it uses to declassify information that is designed to protect sources and methods,” the official said.

The tactic has caused some consternation in U.K. and U.S. intelligence circles, officials said. Mr. Sipher cautioned that he and his colleagues always worry that such releases could eventually lead to disclosures that could harm intelligence gathering. “As an intelligence officer, I’d worry about the source” being exposed, he said. Still, he said, “It’s time for an unusual response.”

—Ann M. Simmons in Moscow contributed to this article.

Write to Max Colchester at max.colchester@wsj.com and Warren P. Strobel at Warren.Strobel@wsj.com