Russian President Vladimir Putin announced the impending deployment Wednesday of a new hypersonic nuclear-capable missile system that he claims will evade American defenses worldwide, dramatically upping the ante of a growing high-tech arms race with Washington.

Moscow has worked for years on the system known as “Avangard,” which is capable of striking targets thousands of miles away, and Mr. Putin boasted that the Russian military has now successfully tested the system with missiles that fly at 20 times the speed of sound — about a mile per second — to render all current missile defense systems obsolete.

The stunning assertion coincides a moment of increased military tension between the U.S. and Russia, as Moscow continues to test the Western resolve with brazen acts of aggression. Analysts say Mr. Putin’s public flaunting of Avangard’s hypersonic capabilities underscored his desire to position Russia as a leader on the global military stage on par with the U.S. and China.

Hypersonic weapons in general represent a serious threat to international stability. National security sources argue the U.S., Russia and China must come together to negotiate and sign a sweeping non-proliferation accord to stop weapons from spreading.

The question now centers on the extent to which Mr. Putin has elevated Moscow’s leverage over any future such negotiations.

“The Avangard is invulnerable to intercept by any existing and prospective missile defense means of the potential adversary,” the Russian president said in a speech Wednesday.

While no other nation, including the United States, has announced the possession of such a system, sources say both Washington and Beijing are currently researching and testing hypersonic weapons.

However, neither has publicly claimed to have succeeded in developing a defense system capable of taking down a hypersonic missile.

To the contrary, Air Force Gen. John Hyten, commander of U.S. Strategic Command, told the Senate Armed Services Committee in March that, “We don’t have any defense that could deny the employment of such a weapon against us.”

Outgoing Defense Secretary James Mattis said earlier this month the U.S. is working on the “next generation” of missile defense systems to detect and defeat hypersonic weapons. But Wednesday’s developments suggest there is little time to spare.

Mr. Putin said the Russian system is set to be deployed next year, claiming it will give Moscow a distinct advantage over its global competitors at a time of growing friction in the Pacific, the Middle East, Africa, and elsewhere around the world.

“From next year, 2019, Russia’s armed forces will get the new intercontinental strategic system Avangard,” the Russian president said. “It’s a big moment in the life of the armed forces and in the life of the country. Russia has obtained a new type of strategic weapon.”

News of the impending deployment marks the latest in an evolving series of what national security sources describe increasingly brazen Russian actions.

Mr. Putin’s announcement came just a month after Russian forces seized Ukrainian vessels traveling through the Kerch Strait and detained the ships’ crews — part of an ongoing effort to exercise control over Russia’s neighbors in the former Soviet bloc.

Moscow also is gaining greater influence in Syria, where U.S. troops are set to return home following a surprise withdrawal announcement from President Trump last week.

Russia’s ongoing alliance with Syrian dictator Bashar Assad gives the Kremlin a potentially strong foothold in the Middle East at a time when the U.S. its reducing its military presence there.

‘We will build it up’

The deployment of Avangard threatens to up the ante in what’s become a Cold War-style arms race between the U.S. and Russia.

The Trump administration has for months warned that Russia is flagrantly violating a key 30-year-old nuclear pact known as the Intermediate-range Nuclear Forces (INF) Treaty, which limits both the U.S. and Russia from building or deploying nuclear-capable missiles and with a range of between 300 and 3,400 miles.

Secretary of State Mike Pompeo announced on Dec. 4 that the administration will officially begin pulling the U.S. out of the treaty in 60 days unless Moscow takes clear steps to come back into compliance.

The announcement came after Mr. Trump had stressed that Washington must preserve its right to keep pace with Russia by building up America’s own capabilities.

“Until people come to their senses, we will build it up,” the president said in October.

The Reagan-era INF deal does not appear to apply explicitly to the Avangard system since the new weapon has a range much greater than 3,400 miles — Mr. Putin claimed that a successful Russian military test of the system involved hitting a target 3,700 miles away.

According to Russia’s state-run TASS News Agency, the Avangard has a range of advantages over more conventional weapons.

“Compared to traditional warheads of intercontinental ballistic missiles, which follow the ballistic trajectory towards their targets, the maneuvering glider warhead travels a part of its flight path at an altitude of several dozen kilometers in the dense layers of the atmosphere,” the news agency said in a description of the system’s missiles.

Russia’s apparent success with the hypersonic missile also shines a light on a broader global arms competition, including that involving China.

A key piece of the Trump administration’s rationale for withdrawing from the INF is to give the U.S. greater flexibility in developing and potentially deploying weapons to counter Chinese aggression — and officials say Beijing also represents a serious threat in the hypersonic domain.

“The Chinese continue to build up their capabilities, their satellite capabilities, their hypersonic capabilities, their artificial intelligence capabilities, the capacity of the [Chinese military] to conduct operations not only in their territory but in a more expeditionary fashion,” Mr. Pompeo told radio host Hugh Hewitt earlier this month.

Defense analysts believe it’s imperative that hypersonic weapons do not spread beyond the U.S., Russia and China.

“Hypersonic missiles are being developed by the United States, Russia, and China. Their proliferation beyond these three could result in other powers setting their strategic forces on hair-trigger states of readiness,” a RAND Corporation study of hypersonic weapons said last year.

“Such proliferation could enable other powers to more credibly threaten attacks on major powers,” the study said. “The unavoidable requirement is for the United States, Russia, and China to agree on a nonproliferation policy.”

• S.A. Miller contributed to this report.