The Kremlin said on Wednesday it will consider U.S. President Joe Biden's proposal to hold a meeting with Russia's President Vladimir Putin, as tensions rise following Russia's military build-up around Ukraine.

In a phone call on Tuesday, Biden proposed the two leaders hold a summit "in the near future" that would come at a time of heightened tensions between the former Cold War rivals. 

"It is early to talk about this meeting in terms of specifics. This is a new proposal and it will be studied," Putin's spokesman Dmitry Peskov told reporters.

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Tensions between Moscow and Washington have escalated in recent weeks, with Russia building up its troops on the border with Ukraine, where government forces have been fighting pro-Russia separatists since the annexation of Crimea in 2014. 

On Wednesday, Ukraine's defense minister claimed that Russia is preparing Crimea for potentially storing nuclear weapons and warned that Moscow could attack Ukraine to ensure water supplies for the annexed peninsula.

While not immediately providing evidence for his assertions, Andrii Taran, speaking to the European Parliament's defence sub-committee in Brussels, also said he could not rule out that Russian forces in Crimea could "undertake substantive military provocations" in 2021.

The U.S. and NATO on Tuesday called on Moscow to withdraw its forces and expressed strong support for Ukraine, accusing Russia of taking "very provocative" actions. 

"We consider the concerns of anyone – including the United States – regarding the movement of our armed forces on Russian territory to be unfounded," Peskov said. 

The Kremlin has repeatedly denied its involvement in the long-simmering conflict and rejected claims that it props up the separatist forces.

A Kremlin statement on Tuesday said the two leaders discussed Ukraine as well as the Iranian nuclear program, Afghanistan peace talks and climate change.

In the call, Biden reiterated U.S. support for Kyiv's pro-West government and urged Russia to "de-escalate tensions," but also offered to hold his first face-to-face talks with Putin on "the full range of issues facing the United States and Russia."

Shortly after, Putin spoke on Tuesday night with Finland's President Sauli Niinisto, who said in a statement that the two had discussed the call with Biden and "the planned meeting of the two presidents."

Finland hosted the last summit between Russian and U.S. leaders in 2018, when Putin met with then-President Donald Trump and has been the venue for several historical meetings of Russian and U.S. leaders.

Biden's invitation for a summit was being hailed in Moscow as a sign that Washington had blinked first in the showdown with Russia over Ukraine.

Leonid Slutsky, a senior Russian lawmaker who chairs the foreign affairs committee in the lower house of parliament, said Biden's call marked "a step away from confrontation to dialogue."

"Such a position meets not only mutual interests, but also the interests of international security," Slutsky said in remarks carried by Russian news agencies. "The good news is that the leaders of the two largest nuclear powers have confirmed their readiness for interaction on issues of strategic stability and arms control."

Observers had said part of the reason for the rising tensions over Ukraine was that the Kremlin was testing Biden, who raised hackles in Russia last month by agreeing with a description of Putin as a "killer."

Putin hit back at the insult, saying "it takes one to know one," then invited Biden to hold an online discussion within days. Biden replied that the two would speak "at some point."

European reaction

Germany added its voice to the dispute on Wednesday, accusing Russia of seeking provocation with its troop build-up along the border with Ukraine.

"My impression is that the Russian side is trying everything to provoke a reaction," German Defense Minister Annegret Kramp-Karrenbauer told ARD public television.

"Together with Ukraine, we won't be drawn into this game," she added.

The growing Russian presence at the Ukrainian border has caused concern in the West in recent days, with the U.S. saying troop levels are at their highest since 2014.

Moscow has said it sent troops to its western borders for combat drills because of "threats" from transatlantic alliance NATO.

U.S., French, British and German diplomats will hold talks in Brussels on Wednesday about the worsening tensions between Ukraine and Russia, as well as the situation in Afghanistan and nuclear negotiations with Iran, the German government said on Wednesday.

During this NATO "quad" meeting, "the foreign ministers of the United States, the United Kingdom and Germany as well as a French representative will meet" and "the main topic of the discussions will be Afghanistan, as well as current developments on the border between Ukraine and Russia and on the nuclear deal with Iran," according to a statement from the German Foreign Ministry.

Warships and military build-up

Ukraine's armed forces on Wednesday rehearsed repelling a tank and infantry attack near the border of Russia-annexed Crimea, the Ukrainian military said in a statement.

It posted video footage, set to rock music, of Ukrainian tanks maneuvering in formation and of soldiers loading and firing artillery pieces.

In a Russian description on Tuesday of its build-up, Defense Minister Sergei Shoigu said Moscow had moved two armies and three paratrooper units to its western border as part of a large snap drill meant to test combat readiness and respond to what he called threatening military action by NATO.

Shoigu said on state TV that the three-week exercise, which he called successful, was due to wrap up in the next two weeks, adding that NATO was deploying 40,000 troops and 15,000 pieces of military equipment near Russia's borders, mainly in the Black Sea and the Baltic regions.

The Western alliance denies any such plans. Russia has regularly accused NATO of destabilizing Europe with its troop reinforcements in the Baltics and Poland since the annexation of Crimea.

A senior U.S. State Department official told reporters: "We know Russia's capacity. This enormous build-up that they've made militarily ... to take aggressive action, but we don't know their intentions obviously," the official said.

Two U.S. warships are due to arrive in the Black Sea this week in response to what U.S. and NATO officials say is the largest massing of Russian forces – with thousands of combat-ready troops – since Moscow seized Crimea from Ukraine.

"We warn the United States that it will be better for them to stay far away from Crimea and our Black Sea coast," Ryabkov said. "It will be for their own good." He called the U.S. deployment a provocation designed to test Russian nerves.