The threat of a nuclear weapon being used is higher now than at any point since the conclusion the World War ll, a top United Nations security expert cautioned this week, calling the matter an “urgent” one that requires global attention.

Renata Dwan, director of the U.N. Institute for Disarmament Research warned in Geneva that the heightened risk comes in large part as a result of disarmament negotiations that have chilled during a two-decade stalemate. But Dwan says the threat is also amplified by the increasing competition between nuclear-armed U.S. and China and other nuke-capable nations issuing plans for modernization.

But how does the arsenal of American -- the only country to use a nuke against an enemy -- compare to those other states?

“Other nuclear-armed states, notably Russia and China, are upgrading their arsenals and have tested, produced and deployed more brand-new weapons than the United States over the past decade,” Kingston Reif, Director of Disarmament and Threat Reduction Policy at the Arms Control Association, told Fox News. “But this does not mean the U.S. has fallen behind. The U.S. military has refurbished and improved nearly all of its existing strategic and tactical delivery systems and many of the warheads they carry, too, last well beyond their planned service life.”

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As it stands, nine countries are known to possess nuclear weapons: the U.S., China, Russia, U.K, France, Israel, Pakistan, India, and murkily, North Korea. However, only the first three countries are believed to possess what is known as the “nuclear triad,” a three-pronged structure that consists of missiles that can be launched from land, air and sea.

Harry Kazianis, a senior director at the Center for National Interest, stressed that while many parts of America’s nuclear arsenal are quite old and were designed decades ago, the U.S. “clearly possesses the most advanced and sophisticated atomic arsenal on the planet.”

“Washington’s nuclear weapons arsenal is so powerful it could bring to an end any nation on the planet in less than 60 minutes if it wanted to—and kill billions of people in the process,” he acknowledged. “That amount of power is almost impossible for the mind to fathom, but it is a reality.”

Nonetheless, others painted a far more dire picture of America's capabilities.

“It is decidedly of a Cold War vintage. It is being asked to keep America safe well beyond its original life span. The land-based portion of the nuclear triad is comprised of Minutemen III missiles that were designed in the 1960s and began deployment in the 1970s,” says John Wood, analyst and author of “Russia: The Asymmetrical Threat to the United States.” “The air-based portion of the nuclear triad relies on, to a large extent, B-52 bombers that have been operated by the United States Air Force since the 1950s. The maritime portion relies on Ohio class submarines that were introduced into service in the 1980s.”

Wood also notes that Russia is "now beginning to field tactical and strategic nuclear weapons systems that will increasingly pose an existential threat to the United States of America.”

“They are predominately mobile, with multiple independent re-entry vehicles," he said. "Increasingly they will be comprised of hypersonic warheads, advanced countermeasures, and arguably some of them will even be capable of being re-directed in-flight by the Russian satellite system GLONASS. The U.S. may have the quantity to currently deter Russia, but, increasingly, it will fail to have the quality to make the threat credible. At some point in the next decade, Russia will have the advantage over the United States.”

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The Trump administration, however, is proposing to broaden the circumstances under which the United States would consider the first use of nuclear weapons, develop two new sea-based, low-yield nuclear options -- and laying the groundwork to grow the size of the arsenal, Reif pointed out.

"The U.S. may have the quantity to currently deter Russia, but, increasingly, it will fail to have the quality to make the threat credible. At some point in the next decade, Russia will have the advantage over the United States.” — John Wood

“In addition, the administration has announced the United States will leave the 1987 Intermediate-Range Nuclear Forces Treaty in August 2019 and expressed hostility towards extending the 2010 New Strategic Arms Reduction Treaty,” Reif said. “In short, the administration is preparing to compete in a new nuclear arms race while simultaneously increasing the likelihood of such a contest.”

But the biggest issue Washington has to contend with when it comes to nuclear upgrade ambitions -- bigger than Russia, China or North Korea -- is cost.

Mark Olson, a defense consultant and former Lieutenant Commander, Combat Systems Officer, and Missile Defense Expert with extensive experience in European Ballistic Missile Defense, noted that the Congressional Budget Office estimates nuclear weapons spending will cost taxpayers $1.2 trillion in inflation-adjusted dollars between fiscal years 2017-2046, or 6 percent of national defense spending.

“Proposals are underway to modernize the U.S. arsenal over the next twenty years; however, cost remains a critical obstacle and one which appears destined to compel budgeteers to hack at innovation in other, arguably more critical, areas,” Olson said.

But is one prong of the triad more a priority than the others? Defense Priorities policy director Benjamin H. Friedman said the answer is simple: submarines.

"the greatest strategic priority for nuclear spending should be the most survivable and capable leg of the triad: submarines,” Friedman said.

Despite the worldwide development, buildup -- and promotion of -- nuclear weapons and their delivery devices, one expert cautions against using the term "arms race," though she concedes "there are certainly things to raise concerns."

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“Both the U.S. and Russia are moving towards investing in modernization and new types of nuclear arsenals," said Bonnie Jenkins, advisor to Foreign Policy for America and former coordinator for Threat Reduction Programs at the International Security and Nonproliferation Bureau at the U.S. Department of State. “There are few avenues for discussion and negotiations between the US and Russia. This is not an environment that gives confidence about a reduction or even keeping the arms at the status quo.”