Since "little green men," as Russia's unmarked troops were popularly known, descended on Ukraine's Crimea peninsula in February 2014, Moscow has been building up its military forces there. Now it could raise tensions further by deploying nuclear weapons to Crimea, officials say, a threat that has riled lawmakers in Washington. According to Kiev, Russian missiles that can carry nuclear warheads have already arrived on the peninsula.

"I don't know if there are nuclear weapons there now. I don't know about any plans, but in principle Russia can do it," said Mikhail Ulyanov, head of arms control for Russia's foreign ministry, when asked this week if Russia would deploy nuclear arms to Crimea. "Naturally Russia has the right to put nuclear weapons in any region on its territory if it deems it necessary."

His comments echoed Russian Foreign Minister Sergei Lavrov, who claimed in December that Crimea was never a "nuclear-free zone" even though Ukraine had given up its atomic weapons by treaty. "Now Crimea has become part of a government that has such weapons in accordance with the non-proliferation treaty," Lavrov said. "And the Russian government has, in accordance with international law, every right to deploy its legitimate nuclear arsenal according to its interests."

Retired Russian Major General Vladimir Dvorkin, who tested the Soviet Union's first nuclear missile submarines, including the ill-fated K-19, told VICE News that there was no "strategic or practical" reason to deploy nuclear missiles to Crimea since it would not further overall nuclear deterrence goals.

"In terms of military security and deterrence, there's no need to put nuclear arms in Crimea … but I'm not a politician, and I can't predict what they might do to solve some sort of political tasks," Dvorkin said.

Russia has already deployed systems to Crimea capable of carrying nuclear weapons, Ukraine's general staff has claimed. In December, it said that a division of Iskander mobile missile launchers, which can be outfitted with nuclear warheads, had entered Crimea. In October, a Ukrainian Twitter account posted photographs from a Russian soldier's social media page showing what it said was an Iskander launcher in Dzhankoi, Crimea.

"I don't know if there are nuclear weapons there now. I don't know about any plans, but in principle Russia can do it."

The Iskander has served as the Kremlin's premier missile threat in the past, and reported deployments of Iskanders to Russia's European exclave of Kaliningrad alarmed Poland and the Baltic States in 2013.

Strategic missiles could be joined in Crimea by tactical nuclear weapons in 2016: The Gvardeiskoye airbase is reportedly being refurbished to host Tupolev Tu-22M3 "Backfire" long-range supersonic bombers, which can carry nuclear payloads.

"We hope that in two years the airbase in Gvardeyskoye will again be the base for a missile-carrying regiment of Tu-22M3," a Russian defense ministry source told Interfax news agency in March 2014.

In addition, a new local branch of the Russian defense ministry's 12th command, which stores, transports and dismantles components of tactical and ballistic nuclear missiles, was reportedly formed in Crimea at the end of January.

Kiev has argued that deploying nuclear weapons to Crimea, which the international community considers to be part of Ukraine, would be in violation of an agreement prohibiting such arms in the country.

"This is a challenge to the whole world, and the world should react with all means and methods to not allow Russia to deploy nuclear weapons on Ukrainian territory, since Crimea is the territory of Ukraine," said Ukrainian Prime Minister Arseniy Yatseniuk.

As part of the Budapest Memorandum signed in 1994 by Ukraine, Great Britain, Russia and the United States, Kiev completely gave up its nuclear arsenal, the third-largest in the world, in exchange for security assurances including a promise to respect the "existing borders of Ukraine." This agreement was violated by Russia when its troops took over Crimea, although the Russian foreign ministry recently claimed that it hadn't broached the agreement, because the peninsula's residents had "exercised the right to self-determination through free expression of will."

Prior to the Budapest agreement, it was rumored that the Soviet Union had a huge arsenal of nuclear missiles and bombs in Crimea to outfit the ships and aircraft of the Black Sea fleet, as well as another stash of atomic torpedoes, artillery shells and cruise missiles.

"This is a challenge to the whole world, and the world should react with all means and methods to not allow Russia to deploy nuclear weapons on Ukrainian territory."

The reported nuclear weapon deployments are part of a "military buildup" in Crimea that was condemned recently by the NATO-Ukraine commission. Moscow has recently begun flexing its military muscle in Crimea and other territories: News agency RIA Novosti reported that Russian units started exercises on Thursday in Crimea, as well as in Abkhazia and South Ossetia, two breakaway republics in Georgia that are defended by Russian troops.

In addition, Moscow has been accused of a nuclear arms buildup after the US State Department said in July it had tested a new ground-launched cruise missile in violation of the Intermediate-Range Nuclear Forces Treaty.

The idea of nuclear weapons in Crimea is not a happy one for Washington and provoked a flurry of debate over possible countermeasures. Republican Congressmen Mike Rogers and Mike Turner, the leaders of the House Armed Services Committee, wrote a letter to then-Defense Secretary Chuck Hagel and Secretary of State John Kerry in January calling the deployment of nuclear weapons to Crimea a "dangerous escalation in Russia's recent aggression" and a "new military threat to US allies and deployed forces in Europe."

The letter demanded the US take action, arguing that the moves to place nuclear bombers and missiles in Crimea showed that "President Putin's aggression has not been checked by economic sanctions nor by the finger-waving of diplomats." Specifically, Rogers and Turner asked about the possibility of establishing bases for US nuclear weapons and aircraft capable of carrying nuclear bombs in NATO states in central and eastern Europe. (The United States reportedly has 160 to 200 B61 nuclear bombs at airfields in Germany, Belgium, the Netherlands, Italy and Turkey.)

But Brookings Institution analyst Steven Pfifer wrote in January that placing US nuclear weapons so close to Russia would contradict NATO Policy and be a "highly provocative" move that could set off a game of brinksmanship comparable to the Cuban missile crisis. Instead, he argued that the United States should station more conventional forces in Europe and supply Ukraine with defensive weapons, a controversial decision that the Obama administration has been considering in recent months.

Russian Academy of Sciences political analyst Alexei Arbatov told the website Vzglyad that Russia would be unlikely to actually deploy nuclear weapons to Crimea and was making statements to that effect to "assert the irreversibility of Crimea joining Russia."

"This is a big political statement. It probably won't be realized in practice," Lieutenant General Viktor Yesin, the former first deputy commander of Russia's Strategic Missile Troops, told the publication.

But Russian political and defense analysts told VICE News that Russia was fully ready to deploy nuclear weapons to Crimea to counter Western military moves in eastern Europe.

"It will depend on NATO's actions," said Alexei Fenenko, a Moscow State University professor of world politics. "If NATO starts to do shows of strength or delivers arms to Ukraine, the Russian response will likely be to deploy nuclear arms (to Crimea)."

"Technically it's all feasible, whether it will be done or not, we don't know. It simply depends on how the West will react," said Ruslan Pukhov of Moscow's Center for Analysis of Strategies and Technologies.