Western leaders launched a volley of condemnations and threatened retaliation for the Russian invasion of Ukraine.

Vladimir Putin on Thursday ordered the entry of troops into the country and asked the army in Kiev to lay down their arms in what many fear will be the worst European conflict since the Second World War.

UN Secretary-General António Guterres has warned that if military action leads to “all-out war”, it will be difficult to predict the number of dead and displaced.

US President Joe Biden has accused Putin of launching a “premeditated war that will result in catastrophic loss of life and human suffering”.

NATO has convened an emergency meeting of its top decision-making body, its leader Jens Stoltenberg denouncing “Russia’s reckless and unprovoked attack on Ukraine, which puts countless civilian lives at risk”.

“In these dark hours, our thoughts are with Ukraine and the innocent women, men and children who face this unprovoked attack and fear for their lives,” said European Commission President Ursula von der Leyen.

Boris Johnson, British Prime Minister, said Putin had “chose a path of bloodshed and destruction in launching this unprovoked attack on Ukraine”, adding: “The UK and our allies will respond decisive way”.

“It’s a terrible day for Ukraine and a dark day for Europe,” German Chancellor Olaf Scholz said. “The Russian attack on Ukraine is a flagrant violation of international law. Germany condemns this irresponsible act by President Putin in the strongest terms.

Zhang Jun, the Chinese envoy to the UN, said the “door to a peaceful solution” had not yet closed and that all parties should exercise restraint.

Ireland, which sits on the UN Security Council, condemned the Russian invasion and demanded strong action from the West.

“Russia has launched a full-scale invasion of Ukraine. May God help them, ” tweeted Simon Coveney, Minister of Foreign Affairs. “Make no mistake, this is a shocking and murderous act of aggression against a sovereign and peaceful state. The EU and the world must react strongly.