Russia has declared war on Ukraine and launched a major offensive from three sides in the biggest attack on a European state since World War Two. On Thursday AEDT, just minutes after Russian President Vladimir Putin appeared on state television to announce the “special military operation”, explosions broke the pre-dawn quiet in the Ukrainian capital, Kyiv, as well as its second-largest city, Kharkhiv, close to the Russian border in the north-east.

At the time of writing, Russian forces had fired missiles at several Ukrainian cities and military centres, landed troops on its south coast from the Black Sea and seized the shuttered Chernobyl nuclear power plant, as more troops spilled over the northern borders with Russia and Belarus. Ukrainians are fighting back to stop “a new Iron Curtain falling” in Europe, as a fresh wave of cyberattacks hit the country. Invading troops are now closing in on Kyiv. Many residents have taken shelter in metro stations deep underground, taking their sleeping bags and dogs with them, as explosions and gunfire ring out in the city above. Others have taken up arms.

Meanwhile, Western leaders have been moving to send aid to Ukraine and unleash tougher sanctions on Russia, including freezing the assets of President Vladimir Putin himself. NATO countries are ramping up their air, land and sea forces in eastern Europe, and Russians have taken to streets back home to protest the war with their neighbour.

Where are the key flashpoints of fighting?

So far, the attack is playing out as the “pincer” move Western intelligence had warned of, with strikes hitting from the north, east, and south as many people flee west. Missiles and rocket fire have rained down across Ukraine, including in the port cities of Odesa in the south and Mariupol in the east (Mariupol is just 20 kilometres from the long-simmering frontline between Ukrainian soldiers and Russian-backed separatists.) Ukraine has declared martial law and mobilised its armed forces, including civilian militias, as it fights back against one of the biggest militaries in the world. Ukraine’s own army has grown in recent years and Western weapons have been flooding in since Russian troops began massing on the border.

Invading forces are marching over the borders in the north with Russia and its ally Belarus (where Russia had been massing troops) and fierce fighting has broken out around Kyiv – the capital is a key prize for Putin as the birthplace of both Ukrainian and Russian cultures. More troops were called in to defend the city on Friday and explosions rang out as Ukrainian forces shot down Russian aircraft and braced for incoming tanks.

Meanwhile, the Ukrainian navy are defending bases and ports in the Black Sea, saying the Russians have begun firing cruise missiles on the coastal cities of Sumy, Poltava and Mariupol. Further inland, intense fighting is raging south of Kyiv as Russian troops try to move up deeper into Ukraine.

The International Atomic Energy Agency has voiced concern after a battle Thursday at the Chernobyl nuclear power plant near the Belarussian border, the site of the disastrous 1986 nuclear meltdown. Russian forces have now taken control of the plant (and reportedly its staff hostage.)

On Friday, Ukrainian President Volodymyr Zelensky said 137 civilians and military personnel were killed in the first day of the invasion. He called them heroes and hit out at Russia’s claim that it was only targeting military assets. “They’re killing people and turning peaceful cities into military targets,” he said, adding Russian sabotage groups had already entered Kyiv searching for political leaders, with Zelensky himself as the number one target.

But, despite fake Russian reports that he had fled the city, the Ukrainian president has so far refused US offers to evacuate him safely from Ukraine, instead staying to help defend the capital. On the second night of the invasion (Saturday AEDT), as Kyiv came further under siege, he said the fate of Ukraine was now being decided. By the morning, Ukrainian authorities said they had pushed back invaders from an army base and a key road near the city. UK officials said the Ukrainian resistance had been extraordinary so far considering the firepower they were up against, and Russia was failing in its initial bid to take key cities.

Audio has also emerged of the moment a Russian warship told Ukraine border guards defending Zmiinyi island in the Black Sea to surrender or be fired on. They responded: “go f*** yourself” and were all killed under Russian fire Thursday as Moscow forces took over the island.

What territories has Russia already claimed?

Announcing the strike Thursday just as United Nations leaders were meeting to urge him back from the brink of war, Putin did not spell out how deep he would ultimately push into Ukraine. But he has previously flagged he intends to take the east, where separatists have been fighting an eight-year war for territory in the Donbas with Russian support. They control less than half of the Donetsk and Luhansk regions but claim sovereignty over the entire area.

Putin officially backed their claim on Tuesday, sending in his own troops, who are now joining separatists in pushing against the frontline with Ukraine. As the strike began, Putin called on Ukrainian soldiers to lay down their arms.

He has also demanded Ukraine cede Crimea in the south, which Russia annexed by force in 2014 when Ukrainian protests toppled the country’s pro-Kremlin president.

How is Russia justifying the attack?

Putin claims the strike is designed to “demilitarise and denazify Ukraine”, not occupy it, but it extends far beyond the eastern territories he has been moving on in recent days and follows repeated denials from Russia that it was planning an attack.

To the UN, Russia justified the strike under article 51 of the UN charter, which allows for “self-defence”. World leaders and media have dismissed Russian claims of Ukrainian aggression and even a “genocide” in the east against Russian-speakers as an invented pretext for war.

Ukraine gave up its nuclear weapons when it became an independent nation after the collapse of Soviet Union (as part of an agreement that Russia would not interfere in Ukrainian sovereignty). And until now Ukrainian soldiers had been reluctant to fire back at the “line of contact” with separatists, where shelling from the rebel side dramatically escalated ahead of the all-out strike. In 2014, Putin also claimed his seizure of the Crimean Peninsula was to protect Russian-speakers from what he called a “fascist coup” and when he sent troops into Georgia in 2008 he called them “peacekeepers” too.

On Thursday, Putin again hit out at the expansion of the Western military alliance NATO, which he has been demanding pull back its forces in eastern Europe and disavow talk of Ukraine ever joining the alliance. He warned the West that any foreign interference in the attack would lead to “such consequences as you have never before experienced in your history. We are ready for any turn of events.”

To Putin, Ukraine is a key battleground in his war for influence with the West, as he looks to reclaim some of Russia’s former Soviet glory.

What has been the response so far?

World leaders are condemning Russia’s attack and have been convening to coordinate responses. Large protests against the war have erupted around the globe (including Moscow itself where many Russian protesters have already been arrested). As the missiles began to rain down, Ukraine called on the world to act, and urged Turkey to close the Black Sea to Russia.

While countries have said they won’t send troops to defend Ukraine, as it is not a member of NATO, some have already been sending in weapons arm its growing army, including anti-tank and anti-aircraft missiles, and many are now pledging further medical aid and supplies. (Australia will send non-lethal military equipment and medical supplies.) Nearby countries Poland and Moldova are already seeing tens of thousands of Ukrainian refugees fleeing over their borders.

Western countries are also ramping up the new wave of economic sanctions on Russia that began this week as Moscow sent troops into the east. New US sanctions, for example, are designed to cut Russia off from most banking markets around the world, though they do not ban it from Swift – the main international payments network (Much of Europe worry it will do too much damage to their own economies.)

Some, including Australia, are also expanding financial sanctions to Belarus, and Russia-wide bans will come into force on sensitive US technologies such as telecommunications and encryption security – a move that US President Joe Biden says will “strike a blow” to Putin’s long-term ambitions to modernise Russia’s military. Germany has already stopped certification of the Nord Stream 2 gas pipeline, which was key to Moscow’s plans to increase energy sales to Europe.

NATO secretary-general Jens Stoltenberg has described the invasion as “a cold-blooded” and “brutal act of war” as the alliance ramps up its defences in nearby member countries. Germany’s Chancellor, Olaf Scholz, said Thursday was “a dark day for Europe” and UK Prime Minister Boris Johnson said he was appalled Putin had opted for “a path of bloodshed and destruction by launching this unprovoked attack on Ukraine”.

Prime Minister Scott Morrison said Russia had chosen war and must pay for it, as Australia moves to join Western allies in sanctioning Putin and his inner circle.

But China, which has been drawing closer to Russia in recent years, notably refused to criticise Russia’s attack on Ukraine. Instead, a foreign ministry spokeswoman repeated calls for peace talks and said: “the Ukraine issue is complex in its historical background.” And, in a step that could blunt the impact of Western economic sanctions, Beijing approved imports of Russian wheat.

Mr Morrison has hit out at China for throwing Moscow a “lifeline” and backed Ukraine’s call to kick Russia out of the SWIFT payment system, along with Johnson and Canadian President Justin Trudeau.

Even as the fighting rages, Ukraine and Russia are discussing further peace talks.

This article has been updated since its first publication on February 24. You can follow our live coverage here.