All-out war is unfolding across Ukraine as Russian forces have invaded the neighboring country.

What are the details?

Ukraine officials say that more than 40 soldiers and up to 10 civilians have been killed thus far in the early hours of the Russian invasion as explosions have rocked cities across Ukraine.

In response to the violent attacks, Ukrainian President Volodymyr Zelenskyy has declared martial law.

Residents have taken to the highways in an attempt to to flee Ukrainian capital Kyiv, while others have taken to subway stations as fortified, improvised bunkers.

Ukraine Prime Minister Volodymyr Zelenskyy condemned the attack, noting that Russia is on a "path of evil," comparing Russian President Vladimir Putin's attack to that of Adolf Hitler.

In Thursday remarks, Zelenskyy called for "everyone who is able" to join the military and called on veterans to help.

Putin took to the airwaves early Thursday morning and issued disturbing threats while detailing the invasion — which he referred to as a "special military operation."

In a series of implausible remarks, he claimed that two "people's republics" — Ukrainian regions of Donbas — of Donetsk and Luhansk "turned to Russian with a request for help."

In response, Putin said, he vowed to "demilitarize" and "deNazify" Ukraine, which he claimed had been subjected to genocide.

"Our actions are self-defense against threats," he falsely claimed. "We do not plan to impose ourselves on anyone. ... NATO supports Ukrainian neo-Nazis ... our actions are self-defense against threats."

He concluded, "Whoever tries to interfere with us, and even more so, to create threats for our country, for our people, should know that Russia's response will be immediate and will lead you to such consequences that you have never experienced in your history. We are ready for any development of events. All necessary decisions in this regard have been made. I hope that I have been heard."

You can read more on the background here.

What else?

European Commission President Ursula von der Leyen vowed to hand down the "harshest ever sanctions" against Russian in response to the "barbaric attack," threatening to "weaken Russia's economic base" as well as its "capacity to modernize."

"We will freeze Russian assets in the European Union and stop the access of Russian banks to European financial markets,” Von der Leyen told reporters during the early hours of Thursday morning. “We condemn this barbaric attack and the cynical arguments that are being used to justify it.”

She added, “These sanctions are designed to take a heavy toll on the Kremlin's interests and their ability to finance war. And we know that millions of Russians do not want war. We will not allow President [Vladimir] Putin to replace the rule of law, by the rule of force, and ruthlessness. Ukraine will prevail."

NATO member states Estonia, Latvia, Lithiuania, and Poland have all triggered NATO Article 4, CNN reported, to "launch consultations within the alliance over Russia's attack on Ukraine."

“The Parties will consult together whenever, in the opinion of any of them, the territorial integrity, political independence, or security of any of the Parties is threatened,” Article 4 of the North Atlantic Treaty states. While Ukraine is not a member of NATO, previous invocations of NATO Article 4 have resulted in a NATO response to include military aid and more.

Later Thursday morning, CNN reported that NATO is set to "increase land, sea, and air forces on its eastern flank" amid the attack.

In a statement, the security alliance said, "Russia’s actions pose a serious threat to Euro-Atlantic security, and they will have geostrategic consequences. NATO will continue to take all necessary measures to ensure the security and defense of all Allies."

“We are deploying additional defensive land and air forces to the eastern part of the Alliance, as well as additional maritime assets," the statement continued. "We have increased the readiness of our forces to respond to all contingencies."

“Today, we have held consultations under Article 4 of the Washington Treaty," the statement concluded. "We have decided, in line with our defensive planning to protect all Allies, to take additional steps to further strengthen deterrence and defense across the Alliance. Our measures are and remain preventive, proportionate and non-escalatory."

President Joe Biden on Wednesday night condemned the attack.

"The prayers of the entire world are with the people of Ukraine tonight as they suffer an unprovoked and unjustified attack by Russian military forces," Biden said in a statement on the invasion. "President Putin has chosen a premeditated war that will bring a catastrophic loss of life and human suffering. Russia alone is responsible for the death and destruction this attack will bring, and the United States and its Allies and partners will respond in a united and decisive way."