Ukrainian officials were set to meet with their Russian counterparts on Monday as tensions continued to mount in the capital, Kyiv, where Ukraine military forces fended off Russian assaults.

Russian President Vladimir Putin on Sunday ordered his country’s nuclear weapons to be prepared for heightened readiness to launch because of what he described as “aggressive statements” by Western adversaries, stoking fears of the possibility of nuclear war.

Putin’s order comes as Ukraine’s outgunned and outnumbered forces have put up a fierce defense across the country, repelling the Russian offensive launched last Wednesday.

But on Monday morning, Russian forces seized two small cities in southeastern Ukraine and the area around a nuclear power plant, then ran into stiff resistance elsewhere.

Having launched the biggest assault on a European state since World War II, Putin put Russia’s nuclear deterrent on high alert Sunday in the face of a barrage of Western-led reprisals for his war on Ukraine.

Blasts were heard before dawn Monday in Kyiv and in the major city of Kharkiv, Ukrainian authorities said. But Russian ground forces’ attempts to capture major urban centers had been repelled, they added.

The Russian leader is reportedly “furious” at the slow-moving invasion that he had expected to be over in a matter of days.

Russia’s commitment to its struggling military invasion will be tested this week as economic sanctions imposed by the United States and its allies take effect Monday after they decided to remove select Russian banks from SWIFT — an international finance network of over 11,000 financial institutions in more than 200 countries — as punishment.

The Russian ruble tanked nearly 30% as markets opened in the east late Sunday, an all-time low versus the American dollar.

The ruble dropped to as low as 119 per dollar, and was last down 28.77% at 118, according to Reuters.

The euro also suffered, dipping  0.76% to $1.11855, after earlier falling as much as 1.34%.

Western nations also pledged to deliver weapons for Ukraine, including machine guns and anti-aircraft missiles. Canada, France, Germany and Portugal were among the countries that have closed their airspace to Russian planes. The EU will also ban certain Russian media outlets, according to European Commission President Ursula von der Leyen.

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Delegations from Ukraine and Russia are expected to meet today for peace talks near a river on the Ukrainian-Belarusian border, according to the office of Ukraine President Volodymyr Zelensky. 

“We agreed that the Ukrainian delegation would meet with the Russian delegation without preconditions on the Ukrainian-Belarusian border, near the Pripyat River,” Zelensky’s office announced on its official Telegram channel.

The prospect of peace talks may be complicated, however, after a US official said Sunday night that Belarus is preparing to send soldiers into Ukraine as soon as today in order to support Russia’s ongoing military campaign in the country, the Washington Post reported.

“It’s very clear Minsk is now an extension of the Kremlin,” the official said, referring to the Belarus capital.

The European Union announced sanctions against the Russian ally on Sunday, criticizing President Alexander Lukashenko’s regime for being “complicit in this vicious attack against Ukraine,” von der Leyen said on Sunday.

It’s unclear when the meeting will take place and what Russia’s demands are. Western officials believe that Putin plans to overthrow the Ukrainian government and replace it with a loyal regime, reasserting Russia’s Cold War-era influence and redrawing the map of Europe.

Meanwhile, Russia continued its multi-front attack on Ukraine with missile strikes reported across the country overnight, killing civilians.

Heartbreaking images emerged Sunday of some of the youngest victims killed in Russia’s war on Ukraine.

Among the gut-wrenching photos from the Ukrainian city of Mariupol in the Donetsk region was a shot of paramedic Oleksandr Konovalov performing CPR in vain on a small girl brought to a city hospital after she was injured during a Russian attack on civilians. Next to her, an adult covered in blood crouches down in agony. 

Their resuscitation efforts failed, and the girl tragically became one of the 16 children who have been killed so far in the war, said Minister of Health Viktor Lyashko, according to the Kyiv Independent.

Russian forces captured Berdyansk, a Ukrainian port city of about 100,000 on the Azov Sea coast, according to Oleksiy Arestovich, an adviser to Zelensky’s office. Mariupol, a city about 50 miles to the south that is considered a prime Russian target, is “hanging on,” Arestovich said. Russian troops also made advances in the city of Kherson, in Ukraine’s south.

Kyiv Mayor Vitali Klitschko said in an interview with the Associated Press on Sunday that Ukraine’s capital was fully “encircled” by Russian troops with no way out — only to try to backtrack hours later by claiming he was the victim of Russian “lies.”

Kyiv, a city of nearly 3 million people, was still in Ukrainian hands after another night of explosions and air raid alarms ringing out through the capital. After hours of calm early Sunday, explosions were heard in the city again at an airport.

“The situation in Kyiv is under Ukrainian control. All Russian efforts to occupy it have failed,” the Ukrainian government announced on its official Telegram channel, boasting “significant personnel losses” from Russian forces as the sun rose in Kyiv on Monday.

“Russian troops are demoralized and exhausted. We have shown that we know how to protect our home from uninvited guests,” the statement said.

Kyiv residents have hunkered down in basements, garages and subway stations during the attacks, as food and medicine supplies are running low, according to the mayor.

In Kharkiv, Ukraine’s second-largest city,  invading Russians have been expelled from the northeastern city after intense fighting Sunday,  Kharkiv’s regional governor Oleh Synyehubov said.

“Control over Kharkiv is completely ours!” Synyehubov wrote on Facebook Sunday, adding the army is working to make sure the city is “completely cleansed of the enemy.”

Ukraine has banned all men between the ages of 18 and 60 from leaving the country and has handed out weapons to anyone who wishes to fight. Prisoners with military experience have been released, and Ukrainian officials have broadcast directions on how to make Molotov cocktails.

While the Ukrainians have put up a fierce resistance and Russia faces fuel and other logistical issues,  a senior US defense official told the Associated Press that will probably change.

“We are in day four. The Russians will learn and adapt,” the official said.

United Nations High Commissioner for Human Rights Michelle Bachelet said Monday 102 civilians have been killed during the ongoing Russian invasion.

The commissioner confirmed 442,000 refugees have fled Ukraine so far.

The UN expects the death toll to skyrocket and for millions of Ukrainian citizens to be displaced because of the ongoing Russia-Ukraine war.

“Most of these civilians were killed by explosive weapons with a wide impact area, including shelling from heavy artillery and multi-launch rocket systems, and airstrikes,” Bachelet said.

“The real figures are, I fear, considerably higher.”

The European Union’s member states have unanimously agreed to take in refugees fleeing the war in Ukraine for up to three years without asking them to apply for asylum first. The UN has estimated that if fighting continues, up to 5 million people could be displaced.

US stocks fell and oil prices topped $100 a barrel briefly Sunday evening as investors anxiously eye the economic impact of sanctions again Russia.

Dow futures fell 570 points while S&P 500 and Nasdaq futures traded lower by 2.25% percent shortly after 11:30 p.m. ET Sunday, according to Fox Business.

With Post wires