KYIV/MARIUPOL. Ukrainian forces battled Russian invaders on three sides on Thursday after Moscow mounted an assault by land, sea and air in the biggest attack on a European state since World War Two.

After Russian President Vladimir Putin declared war in a pre-dawn televised address, explosions and gunfire were heard throughout the morning in Kyiv, a city of 3 million people.

By nightfall, a picture was emerging of fierce fighting across multiple fronts.

An adviser to the Ukrainian presidential office said Russian forces had captured the Chernobyl former nuclear power plant, just 90 km (60 miles) north of the capital, and Hostomel airport in the Kyiv region, where paratroopers had earlier been landed. Heavy exchanges of fire were also taking place in the regions of Sumy and Kharkiv in the northeast and Kherson and Odessa, home to a major city and Ukraine’s most important seaport, in the south.

The highway heading west out of Kyiv was choked with traffic across five lanes as residents fled, fearful of bombardments while stuck in their cars.

Putin told business people in Moscow on Thursday evening he had no choice but to act, while Western leaders condemned the Russian leader and promised sweeping economic sanctions.

“This hideous and barbarous venture of Vladimir Putin must end in failure,” British Prime Minister Boris Johnson told parliament, announcing measures targeting banks, members of Putin’s closest circle and super-rich Russians who enjoy high-rolling London lifestyles.

‘New iron curtain’

The day had begun with missiles raining down on Ukrainian targets and authorities reporting columns of troops pouring across the borders from Russia and Belarus to the north and east, and landing on the southern coasts from the Black Sea and Azov Sea.

The assault brought a calamitous end to weeks of fruitless diplomatic efforts by Western leaders to avert war.

President Volodymyr Zelenskiy called on Ukrainians to defend their country and said arms would be given to anyone prepared to fight.

“What we have heard today are not just missile blasts, fighting and the rumble of aircraft. This is the sound of a new Iron Curtain, which has come down and is closing Russia off from the civilised world,” Zelenskiy said.

In his address, Putin said he had ordered “a special military operation” to protect people, including Russian citizens, subjected to “genocide” in Ukraine - an accusation the West calls baseless propaganda.

“And for this we will strive for the demilitarisation and denazification of Ukraine,” Putin said.

After referring earlier in his speech to Russia’s powerful nuclear arsenal, he also warned: “Whoever tries to hinder us ... should know that Russia’s response will be immediate. And it will lead you to such consequences that you have never encountered in your history.”

US President Joe Biden called the Russian action an “unprovoked and unjustified attack” and EU foreign affairs chief Josep Borrell said: “These are among the darkest hours of Europe since the Second World War.”

EU leaders meeting later will impose new sanctions, freezing Russian assets, halting its banks’ access to European financial markets and hitting “Kremlin interests”, senior officials said.

The Group of Seven leading industrialised nations also met and the White House said Biden would announce new sanctions.

Canada and Switzerland were among a number of other countries to announce new measures targeting Russia. China remained out of step, however, rejecting the description of Russia’s actions as an “invasion”.

Constant blasts

A resident of Kharkiv, Ukraine’s second biggest city and close to the Russian border, said windows in apartment blocks were shaking from constant blasts.

Blasts could be heard in the southeastern port of Mariupol, near a frontline held by Russian-backed separatists in eastern Ukraine. Local authorities said 26 people were being treated for wounds in hospital after an eastern district of the port was shelled and “an attempt by Russian troops to break through” into the city was thwarted.

Civilians in Mariupol packed bags. “We are going into hiding,” a woman said.

Ukrainian forces have downed two Russian helicopters and seven other Russian aircraft and destroyed several Russian trucks, and a platoon from Russia’s 74th Motor Rifles Brigade has surrendered, Ukraine’s ambassador to the United States Oksana Markarova said. Markarova cited earlier figures that Russian attacks had killed 40 Ukrainian servicemen and dozens of civilians. Russia’s defence ministry said it had destroyed 83 land-based Ukrainian targets and had achieved all its goals, according to Interfax news agency.

‘Hang them from bridges’

Even with a full-blown invasion under way, Putin’s ultimate aim is obscure. He said he did not plan a military occupation, only to disarm Ukraine and purge it of nationalists. The outright annexation of such a vast, hostile country could be beyond even Russia’s military capabilities. A senior U.S. defence official said Washington believed the invasion was intended to “decapitate” Zelenskiy’s government.

But it is hard to see Ukrainians accepting any new leadership installed by Moscow.

“I think we must fight all those who invade our country so strongly,” said one man stuck in traffic trying to leave Kyiv. “I would hang every single one of them from bridges.”