KYIV, Ukraine (NewsNation Now) — Russian troops launched their anticipated attack on Ukraine on Thursday, as President Vladimir Putin cast aside international condemnation and sanctions and warned other countries that any attempt to interfere would lead to “consequences you have never seen.”

The invasion began with big explosions before dawn in Kyiv, Kharkiv and Odessa as world leaders decried the start of an invasion that could cause massive casualties, topple Ukraine’s democratically elected government and threaten the post-Cold War balance on the continent.

Now, in a new address Thursday, Putin is defending his actions, saying that Russia “can’t stay idle” on the eastward expansion of NATO near the Russian border. He claims the U.S. and its allies have ignored Russia’s demands to prevent Ukraine from joining NATO and for security guarantees.

“For the U.S. and its allies, it is a policy of containing Russia with obvious geopolitical dividends. For our country, it is a matter of life and death. This is not an exaggeration, it’s a fact,” Putin said. “It’s not only a very real threat to our interests but to the very existence of our state and its sovereignty. It is the red line which we’ve spoken about on numerous occasions. They have crossed it.”

Ukraine’s leadership said at least 40 people have been killed and dozens are wounded thus far in what it called a “full-scale war” targeting the country from the east, north and south.

Russian soldiers seized the area surrounding the former nuclear power plant at Chernobyl, Ukrainian leadership confirmed.

The plant was the site of the world’s worst nuclear accident when a nuclear reactor exploded in April 1986, spewing radioactive waste across Europe. The exploded reactor has been covered by a protective shelter to prevent radiation leak and the entire plant has been decommissioned.

Ukrainian police said Russia has carried out 203 attacks since the beginning of the day

Zelenskyy said the country has severed diplomatic relations with Russia. He said the nation’s security is top priority.

“The army and national solidarity are the mainstay of Ukrainian statehood,” Zelenskyy said. “Our military needs this support. … The future of our Ukrainian people depends on every citizen. Everyone who has combat experience and can join the defense of Ukraine.”

NATO’s chief said the “brutal act of war” shattered peace on the European continent, as the U.S.-led alliance mobilized more troops to move toward Eastern Europe.

“A full-scale war in Europe has begun,” Ukrainian presidential adviser Mykhailo Podolyak said. “Russia is not only attacking Ukraine, but the rules of normal life in the modern world.”

The announcement came as NATO agreed to increase land, sea and air forces on the eastern flank near Ukraine and Russia to maintain full support “for the territorial integrity and sovereignty of Ukraine within its internationally recognized borders, including its territorial waters.”

The Ministry of Internal Affairs of Ukraine announced Thursday a military plane crashed with 14 people on board. Five people have died.

“We woke up in a different world today,” German Foreign Minister Annalena Baerbock said.

President Joe Biden pledged new sanctions to punish Russia for the aggression that the international community had expected for weeks but could not prevent through diplomacy.

“We saw flagrant violations of international law,” Biden said Thursday. “Putin is the aggressor. Putin chose this war.”

The outlook for Ukraine is bleak. Retired Lt. Gen. Richard Newton said the Ukrainian forces are “not a match” for the Russia army. Newton, speaking on a special edition of “NewsNation Prime,” predicted Ukraine could fall to the Russian military in about four days, and thought Russia could have air superiority in the country within a matter of hours.

As the conflict in Ukraine continues, NewsNation will bring Americans the latest developments from abroad and insights into its impact at home throughout our newscasts. We’re dropping the paywall on our live stream so it’s available to everyone. You can watch NewsNation’s programming, including the latest on Ukraine, at the top of the hour from 7 to 10 a.m. and 5 to 11 p.m. ET.