The Pentagon dismissed Russian President Vladimir Putin's claim Thursday that he has "invincible" new nuclear weapons to penetrate U.S. defenses.

"We're not surprised by the statement [by Putin], and the American people should rest assured that we're fully prepared" to defend against attack, Dana White, the Pentagon's chief spokesperson, said at a briefing.

"We're prepared to defend this nation no matter what" Putin might add to his arsenal of nuclear weapons, she added at the Pentagon.

Russian President Vladimir Putin boasted Thursday of new nuclear weapons in development or already in his arsenal that will make U.S. and NATO missile defenses obsolete.

The new doomsday weapons include a low-flying stealthy cruise missile with unlimited range and a hypersonic ballistic missile that "will be practically invulnerable. No defense systems will be able to withstand it," Putin said.

In a fiery speech to his rubber-stamp parliament, Putin also said that Russia is developing a high-speed underwater drone to take out enemy submarines.

Putin claimed that the new weapons give Russia dominance in the arms race with the U.S. and render meaningless Washington's attempts to develop counter-measures.

"Efforts to contain Russia have failed, face it," he said.

There was no immediate response from the White House or the Defense Department to Putin's claims that followed the unveiling last month of the U.S. Nuclear Posture Review (NPR). The review called for the development of a new nuclear Sea-Launched Cruise Missile (SLCM) and a new tactical nuclear warhead for submarine-launched ballistic missiles.

On Wednesday, Air Force Gen. John Hyten, commander of U.S. Strategic Command, called Russia the only "existential threat" to the U.S.

In an address to a conference organized by the Association of the U.S. Army on missile defenses, Hyten said the modernization of U.S. nuclear forces called for in the NPR includes improvements to U.S. missile defenses, but "we still have exploitable holes."

In his "State of the Nation" address, Putin said his claims about new nuclear weapons are intended to counter what he charged were provocations in the NPR.

"We are greatly concerned by some parts of the new nuclear posture, which reduces the benchmark for the use of nuclear weapons," he said.

"Whatever soothing words one may try to use behind closed doors, we can read what was written. And it says that these weapons can be used in response to a conventional attack or even a cyber-threat," he added.

Putin warned, "It is my duty to state this: Any use of nuclear weapons against Russia or its allies, be it small-scale, medium-scale or any other scale, will be treated as a nuclear attack on our country. The response will be instant and with all the relevant consequences."

Joseph Cirincione, president of the Ploughshares Fund and an arms control specialist, said in a Tweet, "Welcome to the new arms race. This will not end well."

Cirincione noted that Putin showed graphics of a multi-warhead Intercontinental Ballistic Missile (ICBM) going over the South Pole. "Why south? Our anti-missile radars and interceptors are in the north," he said.

Putin claimed that Russia conducted a test of the new cruise missile last last year. He said the missile was powered by a nuclear engine to give it unlimited range. He said the cruise missile is an example of Russian technological prowess that had been ignored by the West.

"No one listened to us," he said. "Listen to us now."

In outlining the NPR last month, Defense Secretary Jim Mattis anticipated claims by adversaries such as Russia that the U.S. by developing new nuclear weapons is lowering the threshold for their use in war.

"In no way does this approach lower the nuclear threshold," Mattis said. "Rather, by convincing adversaries that even limited use of nuclear weapons will be more costly than they can tolerate, it in fact raises that threshold."

-- Richard Sisk can be reached at Richard.Sisk@Military.com.