Russia unleashed all-out war on Ukraine from land, sea and air on Thursday, attacking targets all around the country including the capital Kiev, pushing Europe towards its most ruinous conflict since 1945 and prompting international fury at the actions of president Vladimir Putin.

       Officially, at least 40 Ukrainian lives, including civilians, have already been lost to the conflict, but that number is certain to grow much higher as the fighting rages and fears mount that it could escalate beyond Ukraine’s borders.

       Reaction to the invasion was immediate: Nato rushed to bolster support to members of the alliance located close to Russia; western leaders unveiled a new package of sanctions against Moscow; European nations warned of a looming refugee crisis; and energy prices jumped while global stock markets tumbled.

       The attack was launched after months of Russia building up troops along Ukraine’s borders - forces it long claimed were on exercise - and after weeks of denial that they would invade. The devastating assault began early on Thursday morning with a defiant Mr Putin, head of the country with a huge arsenal of nuclear warheads, warning the international community not to interfere as the repercussions would be severe.

       “If you do you will face consequences greater than any of you have faced in history,” he said.

       Recommended In pictures: Russia declares war on Ukraine Russia’s Ukraine invasion: ‘A rather terrible conflict is looming’ Ukraine: Belarus says its troops could support Russian invasion ‘if needed’

       He vowed “to defend people who have been victims” of “the Kiev regime” and “demilitarise and de-Nazify Ukraine” - tapping into a long-standing Russian narrative that suggests the country is being subjugated by right-wing radicals.

       Within hours of the invasion being ordered, missile strikes were fired against key military and infrastructure targets inside Ukraine. Luhansk, Sumy and Chernihiv, in the east of Ukraine, were all subjected to attacks, while tanks battled on the outskirts of Kharkiv, after paratroopers dropped in, local reports say.

       Russian forces are also attempting to seize the Chernobyl nuclear plant, the site of the world's worst nuclear accident, according to Ukrainian president Volodymyr Zelensky. “Our defenders are giving their lives so that the tragedy of 1986 will not be repeated,” he said. “This is a declaration of war against the whole of Europe.” One Kiev official said the heavy fighting could disturb nuclear waste at the site.

       An amphibious assault on the key port city of Mariupol has meanwhile been launched, and ground forces are now moving in across the country from Russia, Crimea and its vassal state, Belarus, which is situated close to Kiev. Another key city, Odessa, was also said to be under attack.

       A Ministry of Defence intelligence update, issued from Kiev at 4pm, said Russia’s air strikes had targeted military infrastructure - especially command and control and air defence installations - and that the Ukrainian forces had "put up a staunch resistance and continue to hold key cities".

       (AFP via Getty Images)

       In the capital, where almost three million people live, air sirens forced residents to desperately seek shelter in the city’s underground. Bomb explosions were heard close to Kiev itself, including an air assault attack on Hostomel Airport.

       Roads were packed with people trying to leave the capital to somewhere that might be safer.

       According to a senior US defence official, Russian troops are making a move on Kiev, where a local curfew has now been imposed, and intend to overthrow the national government, Reuters reported. Other urban population centres are in the crosshairs of president Putin, the outlet says, despite insistence from the Kremlin that it had no intention to occupy Ukraine.

       Footage has emerged of dogfights between Ukrainian and Russian jets, with Kiev claiming to have brought down seven aircraft. Social media videos showed apartment buildings hit in residential areas in Kharkhiv, northeast Ukraine, and scores of Ukrainians queuing up to donate blood.

       Ukrainians have begun to flee the county’s main urban centres, including the capital and south-western city of Mariupol.

       Those who have remained say they have been able to access food and water, but this could soon change after Ukraine's military suspended commercial shipping at its ports, stoking fear of supply disruption from the leading grain and oilseeds exporters.

       Mr Zelensky urged citizens to defend the country from Russian forces and said weapons would be issued to everyone who comes forward.

       The attack brought swift - and furious - international condemnation.

       US President Joe Biden accused Russia of an “unprovoked and unjustified attack” and said: “The world will hold Russia accountable.”

       Germany’s Chancellor Olaf Scholz, fast emerging as the strongest European critic of Moscow, said the Russian leader “was endangering the lives of countless innocent people” and pinned the blame on Mr Putin. He added: “For all that there is no justification. This is Putin’s war”.

       The G7 nations were meeting to decide on a response, while outside Downing Street Ukrainians protested.

       Boris Johnson called the invasion “a catastrophe for our continent”, while France’s Emmanuel Macron said it marked “a turning point in the history of Europe”.

       A woman with her daughter waits for a train as they try to leave Kiev

       (AP)

       Nato, which has agreed to reinforce land and air forces on the alliance’s eastern flank near Ukraine and Russia, called the invasion “deliberate and cold-blooded”. However, it said it would not send troops into Ukraine at this stage.

       The European Union has vowed to enforce more sanctions, while all western nations are coming under pressure to impose much tougher punitive measures on Moscow.

       European Commission foreign policy chief, Josep Borrell, described the move as “among the darkest hours of Europe since the end of World War II.”

       British prime minister Boris Johnson is meanwhile rallying European leaders to sever the continent’s dependence on Russian oil, which has given the Kremlin a “grip” on Western politics, and “hobble” the country’s economy.

       As part of the package of sanctions unveiled by Mr Johnson, Aeroflot will imminently be banned from touching down planes in the UK, while there will be an asset freeze on all major Russian banks, including immediately against VTB.

       The UK will also move prohibit a wide range of hi-tech exports to Russia, including semi-conductors, aircraft parts, such as Rolls Royce jet engines, and oil refinery equipment, Mr Johnson said.

       "Putin will stand condemned in the eyes of the world and of history. He will never be able to cleanse the blood of Ukraine from his hands," the prime minister told MPs.

       However, questions have been raised over what impact sanctions will realistically have. Following a series of bilateral agreements recently signed by Moscow and Beijing, Chinese customs have cleared the way for the import of wheat from all over Russia, offering a potential bulwark against the West’s punitive measures.

       Recommended Vladimir Putin launches Russia-Ukraine war - follow live What are the issues between Ukraine and Russia? The crisis explained

       A Kremlin spokesman shrugged off threats from Western leaders and said Russia could not be placed behind an “Iron Curtain” once more.

       This is the second time that Moscow has launched a significant military incursion into Ukraine since the country gained independence from the Soviet Union in 1991, and comes eight years after the annexation of the Crimean peninsula in the south.