KYIV, Ukraine >> Russia launched a wide-ranging attack on Ukraine on Thursday, hitting cities and bases with airstrikes or shelling, as civilians piled into trains and cars to flee. Ukraine’s government said Russian tanks and troops rolled across the border in what it called a “full-scale war” that could rewrite the geopolitical order and whose fallout already reverberated around the globe.

In announcing a major military operation, Russian President Vladimir Putin deflected global condemnation and cascading new sanctions — and chillingly referred to his country’s nuclear arsenal as he threatened any foreign country attempting to interfere with “consequences you have never seen.”

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.

Sirens rang out in Ukraine’s capital and people massed in train stations and took to roads, as the government said the former Soviet republic was seeing a long-anticipated invasion from the east, north and south and reported more than 40 soldiers had been killed and dozens wounded.

“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.”

World leaders decried the attack, which could cause massive casualties, topple Ukraine’s democratically elected government, upend the post-Cold War security order and result in severe economic impact around the world from soaring heating bills to spikes in food prices.

“We woke up in a different world today,” Germany’s foreign minister said, as NATO agreed to beef up air, land and sea forces on its eastern flank near Ukraine and Russia.

Global financial markets plunged and oil prices soared, and governments from the U.S. to Asia and Europe readied new sanctions after weeks of failed efforts for a diplomatic solution. But global powers have said they will not intervene militarily to defend Ukraine.

Ukrainian President Volodymyr Zelenskyy cut diplomatic ties with Moscow and declared martial law. Ukrainians who had long braced for the prospect of an assault were urged to stay home and not to panic, even as officials said Russian troops were rolling into Ukraine, and big explosions were heard in the capital of Kyiv, Kharkiv in the east and Odesa in the west.

“We are facing a war and horror. What could be worse?” 64-year-old Liudmila Gireyeva said in Kyiv. She planned to head to the western city of Lviv and then to try to move to Poland to join her daughter. Putin “will be damned by history, and Ukrainians are damning him.”

After weeks of denying plans to invade, Putin justified his actions in an overnight televised address, asserting that the attack was needed to protect civilians in eastern Ukraine — a false claim the U.S. had predicted he would make as a pretext for an invasion. He accused the U.S. and its allies of ignoring Russia’s demands to prevent Ukraine from joining NATO and for security guarantees.

His spokesman said Thursday that Russia does not intend to occupy Ukraine but will move to “demilitarize” it.

NATO Secretary-General Jens Stoltenberg told reporters in Brussels: “This is a deliberate, cold-blooded and long-planned invasion. … Russia is using force to try to rewrite history.”

The attacks came first from the air. Later Ukrainian authorities described ground invasions in multiple regions, and border guards released security camera footage Thursday showing a line of Russian military vehicles crossing into Ukraine’s government-held territory from Russian-annexed Crimea.

An Associated Press photographer in Mariupol heard explosions and saw dozens of people with suitcases heading for their cars to leave the city. Another AP reporter saw the aftermath of an explosion in Kyiv. AP reporting elsewhere in Ukraine found other damage.

The Russian military claimed to have wiped out Ukraine’s entire air defenses in a matter of hours, and European authorities declared the country’s air space an active conflict zone. Russia’s claims could not immediately be verified, nor could Ukrainian ones that they had shot down several Russian aircraft. The Ukrainian air defense system and air force date back to the Soviet era and are dwarfed by Russia’s massive air power and precision weapons.

U.S. President Joe Biden pledged new sanctions to punish Russia for the “unprovoked and unjustified attack.” The president said he planned to speak to Americans on Thursday after a meeting of the Group of Seven leaders. More sanctions against Russia were expected to be announced.

Zelenskyy urged global leaders to provide defense assistance to Ukraine and help protect its airspace, and urged his compatriots to defend the nation. Ukraine’s Foreign Minister Dmytro Kuleba pleaded: “The world can and must stop Putin. The time to act is now.”

In the capital, Mayor Vitaly Klitschko advised residents to stay home unless they are involved in critical work and urged them to prepare go-bags with necessities and documents if they need to evacuate.

Anton Gerashchenko, an adviser to Ukraine’s interior minister, said on Facebook that the Russian military had launched missile strikes on Ukrainian military command facilities, air bases and military depots in Kyiv, Kharkiv and Dnipro.

The Russian Defense Ministry said it was not targeting cities, but using precision weapons and claimed that “there is no threat to civilian population.”

The consequences of the conflict and resulting sanctions on Russia started reverberating throughout the world.

World stock markets plunged and oil prices surged by nearly $6 per barrel. Market benchmarks tumbled in Europe and Asia and U.S. futures were sharply lower. Brent crude oil jumped to over $100 per barrel Thursday on unease about possible disruption of Russian supplies. The ruble sank.

Anticipating international condemnation and countermeasures, Putin issued a stark warning to other countries not to meddle.

In a reminder of Russia’s nuclear power, Putin warned that “no one should have any doubts that a direct attack on our country will lead to the destruction and horrible consequences for any potential aggressor.”

Putin’s announcement came just hours after the Ukrainian president rejected Moscow’s claims that his country poses a threat to Russia and made a passionate, last-minute plea for peace.

“The people of Ukraine and the government of Ukraine want peace,” Zelenskyy said in an emotional overnight address, speaking in Russian in a direct appeal to Russian citizens. “But if we come under attack, if we face an attempt to take away our country, our freedom, our lives and lives of our children, we will defend ourselves.”

Zelinsky said he asked to arrange a call with Putin late Wednesday, but the Kremlin did not respond.

In an apparent reference to Putin’s move to authorize the deployment of the Russian military to “maintain peace” in eastern Ukraine, Zelensky warned that “this step could mark the start of a big war on the European continent.”

“Any provocation, any spark could trigger a blaze that will destroy everything,” he said.

The attack began even as the U.N. Security Council was holding an emergency meeting to hold off an invasion. Members still unaware of Putin’s announcement of the operation appealed to him to stand down. U.N. Secretary-General Antonio Guterres opened the meeting, just before the announcement, telling Putin: “Give peace a chance.”

European Council President Charles Michel and European Commission President Ursula von der Leyen later promised to hold the Kremlin accountable.

“In these dark hours, our thoughts are with Ukraine and the innocent women, men and children as they face this unprovoked attack and fear for their lives,” they said on Twitter.