Notably, Belarus is one of the closest allies of Putin and shares land border with three North Atlantic Treaty Organization (NATO) countries of Latvia, Lithuania, and Poland. In the initial phase of the Russian invasion of Ukraine, Belarus had also served as a staging ground for the invasion.

Putin's announcement comes as a warning to the West that's stepping up support to Ukraine. NATO members Poland and Slovakia lately announced they would send MiG-29 fighter planes to Ukraine. However, Putin said the move was triggered by the United Kingdom's decision this week to provide Ukraine with armour-piercing rounds containing depleted uranium. He falsely claimed that the rounds have nuclear components.

Putin subsequently toned down his language, but insisted in a state television interview broadcast Saturday night that the ammunition posed an additional danger to both troops and civilians in Ukraine.?

Putin's nuclear sabre-rattling comes after a period in which such comments had stopped. Earlier, Putin had said that "all options" remained on the table with Russia, hinting at the potential use of nuclear weapons. Earlier, Russian partner China too had said the usage of nuclear weapons was out of the question.

What did Putin say?

Putin didn't say how many nuclear weapons Russia would keep in Belarus. The US government believes Russia has about 2,000 tactical nuclear weapons, which include bombs that can be carried by tactical aircraft, warheads for short-range missiles and artillery rounds.

In his interview, Putin argued that by deploying its tactical nuclear weapons in Belarus, Russia was following the lead of the United States, noting that the US weapons are based in Belgium, Germany, Greece, Italy, the Netherlands, and Turkey.

He said, "We are doing what they have been doing for decades, stationing them in certain allied countries, preparing the launch platforms and training their crews. We are going to do the same thing."

Tactical nuclear weapons are intended for use on the battlefield, unlike more powerful, longer-range strategic nuclear weapons. Russia plans to maintain control over the ones it plans to Belarus, and construction of storage facilities for them will be completed by July 1, Putin said.

Russia has stored its tactical nuclear weapons at dedicated depots on its territory, and moving part of the arsenal to a storage facility in Belarus would up the ante in the Ukrainian conflict by placing them closer to the Russian aircraft and missiles already stationed there.

Some hawkish commentators in Russia long have urged the Kremlin to put the tactical nuclear weapons close to the weapons to send a signal to the West about the readiness to use them.

Putin said Belarusian President Alexander Lukashenko has long asked for the nuclear weapons as a counter to NATO. Belarus shares borders with three NATO members — Latvia, Lithuania and Poland — and Russia used its territory as a staging ground to send troops into Ukraine on Feb. 24, 2022.

Putin noted that Russia helped modernize Belarusian military aircraft last year to make them capable of carrying nuclear warheads. He said 10 such planes were ready to go. He said nuclear weapons also could be launched by the Iskander short-range missiles that Russia provided to Belarus last year.?

While discussing in his state TV interview the depleted uranium rounds that Britain promised to ship to Ukraine, Putin charged the ammunition would leave a radioactive trace and contaminate agricultural land.

“Those weapons are harmful not just for combatants, but also for the people living in those territories and for the environment,” he said.

Putin added that Russia has vast stockpiles of similar ammunition but so far has refrained from using them.

Depleted uranium is a byproduct of the uranium enrichment process needed to create nuclear weapons. The rounds can't generate a nuclear reaction but they do emit low levels of radiation. The U.N. nuclear watchdog has warned of the possible dangers of exposure.?

Such rounds were developed by the U.S. during the Cold War to destroy Soviet tanks, including the same T-72 tanks that Ukraine now faces in its push to break through a stalemate in the east.?

Reactions to Putin's announcement

Belarusian opposition leader Sviatlana Tsikhanouskaya, who is living in exile, said the agreement to transfer the tactical nuclear weapons to Belarus “underlines the threat to regional security” from Lukashenko's regime.?

“Europe won't be safe until Belarus dictator is removed; brought before tribunal to face justice for crimes against our country; Ukraine," Tsikhanouskaya wrote in English on Twitter.?

Reactions from Western leaders were not immediately available.?

Observers noted that Putin's announcement came shortly after Chinese President Xi Jinping's visit to Russia and meeting with Putin.

BBC Russia Editor Steve Rosenberg tweeted, "21 Маrch: Russia and China state: 'All nuclear powers must not deploy their nuclear weapons beyond their national territories & must withdraw all nuclear weapons deployed abroad'. 25 March, Putin states: Russia planning to station tactical nuclear weapons in Belarus."

(With AP inputs)