Ukrainian President Volodymyr Zelenskyy urged for a sensible and toned down approach to ongoing tensions with Russia and the Western bloc's warnings that an invasion is imminent, calling for a meeting with his Russian counterpart Vladimir Putin to have a clearer understanding of Moscow's demands.

"I don't know what the president of the Russian Federation wants, so I am proposing a meeting," Zelenskyy said at the Munich Security Conference, where he also met with United States Vice President Kamala Harris. Zelenskyy said Russia could pick the location for the talks.

"Ukraine will continue to follow only the diplomatic path for the sake of a peaceful settlement."

There was no immediate response from the Kremlin.

Zelenskyy spoke hours after separatist leaders in eastern Ukraine ordered a full military mobilization on Saturday while Western leaders made increasingly dire warnings that a Russian invasion of its neighbor appeared imminent.

The Ukrainian was addressing senior Western security officials amid reports of explosions inside Russian territory to Ukraine's east, and in breakaway regions of Ukraine.

"What was shown yesterday in the temporarily occupied territories, some shells allegedly flying from our side, some flying all the way to Rostov, these are pure lies," he said. "They are blowing up something on their side."

He urged Western countries not to wait for a possible Russian invasion to impose sanctions on Russia.

In new signs of fears that a war could start within days, Germany and Austria told their citizens to leave Ukraine. German air carrier Lufthansa canceled flights to the capital, Kyiv, and to Odessa, a Black Sea port that could be a key target in an invasion.

NATO’s liaison office in Kyiv said it was relocating staff to Brussels and to the western Ukraine city of Lviv. Meanwhile, top Ukrainian military officials came under a shelling attack during a tour of the front of the nearly eight-year separatist conflict in eastern Ukraine.

The officials fled to a bomb shelter before hustling from the area, according to an Associated Press journalist who was on the tour.

Violence in eastern Ukraine has spiked in recent days as Ukraine and the two regions held by the rebels each accused the other of escalation. Russia on Saturday said at least two shells fired from a government-held part of eastern Ukraine landed across the border, but Ukrainian Foreign Minister Dmytro Kuleba dismissed that claim as "a fake statement."

Sporadic violence has broken out for years along the line separating Ukrainian forces from the Russia-backed rebels, but the recent shelling and bombing spike could set off a full-scale war.

The United States and many European countries have alleged for months that Russia, which has moved about 150,000 troops near the Ukrainian border, is trying to create pretexts to invade.

"They are uncoiling and are now poised to strike," U.S. Defense Secretary Lloyd Austin said Saturday during a visit to Lithuania.

Harris opened her meeting with Zelenskyy by saying the world was at "a decisive moment in history."

"National borders should not be changed by force," she said, warning Moscow against attempts to redraw Europe's borders.

"We have prepared economic measures that will be swift, severe, and united," she said. "We will target Russia's financial institutions and key industries."

Earlier Saturday, Denis Pushilin, the head of the pro-Russia separatist government in Ukraine's Donetsk region, cited an "immediate threat of aggression" from Ukrainian forces in his announcement. Ukrainian officials vehemently denied having plans to take rebel-controlled areas by force.

"I appeal to all the men in the republic who can hold weapons to defend their families, their children, wives, mothers," Pushilin said. "Together we will achieve the coveted victory that we all need."

A similar statement followed from his counterpart in the Luhansk region. On Friday, the rebels began evacuating civilians to Russia with an announcement that appeared to be part of their and Moscow’s efforts to paint Ukraine as the aggressor.

German Foreign Minister Annalena Baerbock said the evacuation orders could be a tactic to provide the spark for a broader attack.

"To say it very clearly, Ukraine did not give any grounds for the evacuation that was ordered yesterday," she said. "Those are the facts on the ground. We must not allow supposed reasons for war to be constructed out of hot air."

U.S. President Joe Biden said late Friday that based on the latest American intelligence, he was now "convinced" that Russian President Vladimir Putin has decided to invade Ukraine and assault the capital.

"As of this moment, I’m convinced he’s made the decision," Biden said. "We have reason to believe that." He reiterated that the assault could occur in the "coming days."

Meanwhile, Russia conducted massive nuclear drills on Saturday. The Kremlin said Putin, who pledged to protect Russia’s national interests against what it sees as encroaching Western threats, was watching the drills together with Belarusian President Alexander Lukashenko from the situation room.

Notably, the planned exercise involves the Crimea-based Black Sea Fleet. Russia annexed the Crimean Peninsula after seizing it from Ukraine in 2014. .

Underscoring the West's concerns of an imminent invasion, a U.S. defense official said an estimated 40% to 50% of the ground forces deployed in the vicinity of the Ukrainian border have moved into attack positions closer to the border.

The shift has been underway for about a week, other officials have said, and does not necessarily mean Putin has decided to begin an invasion. The defense official spoke on condition of anonymity to discuss internal U.S. military assessments.

The official also said the number of Russian ground units known as battalion tactical groups in the border area had grown to as many as 125, up from 83 two weeks ago. Each group has 750 to 1,000 soldiers.

Lines of communication between Moscow and the West remain open: the American and Russian defense chiefs spoke Friday. French President Emmanuel Macron scheduled a phone call with Putin on Sunday. U.S. Secretary of State Antony Blinken and Russian Foreign Minister Sergey Lavrov agreed to meet next week.

Immediate worries focused on eastern Ukraine, where Ukrainian forces have been fighting the pro-Russia rebels since 2014 in a conflict that has killed some 14,000 people. Violations of a 2015 ceasefire agreement, including shelling and shooting along the line of contact, have been common.

A car bomb exploded in the center of the rebel-controlled city of Donetsk on Friday. Adding to the tensions, two explosions shook the rebel-controlled city of Luhansk early Saturday. No injuries were reported in the incidents.

Ukraine’s military said two of its soldiers died in firing from the rebel side on Saturday.

By Saturday morning, the separatists in the Luhansk and Donetsk regions, which form Ukraine's industrial heartland known as the Donbas, said that thousands of residents of the rebel-controlled areas had been evacuated to Russia.

Russia has issued about 700,000 passports to residents of the rebel-held territories. Claims that Russian citizens are being endangered might be used as justification for military action.

Pushilin, the head of the Donetsk rebel government, alleged in a video statement that Ukraine was going to order an imminent offensive in the area.

Metadata from two videos posted by the separatists announcing the evacuation show that the files were created two days ago, the Associated Press (AP) confirmed. U.S. authorities have alleged that the Kremlin's effort to come up with an invasion pretext could include staged, prerecorded videos.

Authorities in Russia's Rostov region, which borders eastern Ukraine, declared a state of emergency because of the influx of evacuees. Media reports on Saturday described chaos at some of the camps assigned to accommodate the people from eastern Ukraine. The reports said there were long lines of buses and hundreds of people waiting in the cold for hours on end to be housed without access to food or bathroom facilities.

Putin ordered the Russian government to offer 10,000 rubles (about $130) to each evacuee, an amount equivalent to about half of an average monthly salary in eastern Ukraine.

Russia has said that for its own long-term security it needs a commitment that Kyiv will never join the NATO military alliance.

Both Ukraine and NATO members have refused to rule out Kyiv one day joining the alliance, though few expect that soon.

But, referring to an explosion at a kindergarten in the occupied east, Zelenskyy urged delegates not to let the rhetoric obscure the plight of ordinary people.

"Those kids aren't heading towards NATO. They are heading to their classrooms," he said.

Many delegates at the conference called for a de-escalation by Putin, who on Saturday presided over a nuclear preparedness exercise involving firing ballistic missiles.

"History has not yet been written: there is an exit that the Russian government can choose at any time," said Baerbock after a meeting of Western foreign ministers.

"Our common message to them is very clear: Don't make this fatal mistake. Withdraw your troops ... Let's talk."

German Chancellor Olaf Scholz said Putin appeared to be guided by a particular understanding of history in his approach to Ukraine, but warned that down that path lay endless conflict.

"Putin has clearly been dabbling lately in Russian history," Scholz said, pointing to Putin's published texts lamenting the collapse of the Soviet Union and demise of "historical Russia" as well as his talks with the Russian leader this week.

He also dismissed Putin's talk of a genocide in east Ukraine as "ridiculous."

The Russian foreign ministry retorted that Scholz's remark was "unacceptable," according to Interfax news agency.

Chinese Foreign Minister Wang Yi, whose country and Russia are diplomatically aligned, had harsh words for all sides in the dispute, seeing a revived "Cold War mentality" in the confrontation. He said no country, not even a superpower, should replace international norms with its own will.

But British Prime Minister Boris Johnson drew a parallel between Russia's intentions towards Ukraine and China's towards Taiwan, arguing that Western leaders had a duty to be firm.

"If Ukraine is invaded, the shock will echo around the world. And those echoes will be heard in east Asia and will be heard in Taiwan," he said. "People would draw the conclusion that aggression pays, and that might is right."