Vladimir Putin has ordered his military to put Russia’s nuclear deterrence forces on high alert, in the latest signal from the Russian leader that he is prepared to resort to the most extreme level of brinkmanship is his effort to achieve victory in Ukraine. The US accused Putin of “totally unacceptable” escalation and made clear that it would keep up its support of Ukraine and punitive measures on Russia. With the EU also announcing unprecedented new measures against Moscow, it was clear that Putin’s assault on Ukraine had failed to yield the quick victories he had anticipated but had instead rallied a concerted western response that was potentially devastating for Russia’s economy. The Ukrainian president, Volodymyr Zelenskiy, announced that a delegation from Kyiv would meet Russian officials without preconditions on his country’s border with Belarus, but it was far from clear Putin was ready to entertain talks that did not involve compliance with his demands that Ukraine accept partition and disarm. “I do not really believe in the outcome of this meeting, but let them try, so that later not a single citizen of Ukraine has any doubt that I, as president, tried to stop the war,” Zelenskiy said. In the absence of a quick military breakthrough, Putin signalled he was prepared to escalate his onslaught on Ukraine, while taking the unprecedented step of explicitly brandishing Russia’s nuclear arsenal in an effort to deter western support for Ukraine. On Sunday, however, that support continued to grow. The EU announced it would fund weapons supplies to the Ukrainian armed forces, block European airspace to all Russian aircraft including the private jets of oligarchs, and banned the Kremlin’s propaganda channel RT, and its news agency, Sputnik BP announced it would divest its nearly 20% stake in the Russian oil corporation Rosneft Turkey declared that it would close the Bosphorus and Dardanelles straits to the Russian navy, stopping its vessels moving between the Mediterranean and the Black Sea. Sweden will send military aid to Ukraine, including anti-tank weapons, helmets and body armour, its prime minister, Magdalena Andersson, said on Sunday. Putin’s nuclear order came at a meeting between the president, the defence minister, Sergei Shoigu, and the chief of the general staff of the armed forces of Russia, Valery Gerasimov. “Senior officials of the leading Nato countries also allow aggressive statements against our country, therefore I order the minister of defence and the chief of the general staff [of the Russian armed forces] to transfer the deterrence forces of the Russian army to a special mode of combat duty,” Putin said in televised comments. “Western countries aren’t only taking unfriendly actions against our country in the economic sphere, but top officials from leading Nato members made aggressive statements regarding our country.” The Nato secretary general, Jens Stoltenberg, told CNN, in reaction to Putin’s decision to put Russia’s nuclear forces on high alert: “This is dangerous rhetoric. This is a behaviour which is irresponsible.” Putin has told foreign countries not to interfere in his invasion of Ukraine, saying it could lead to “consequences they have never seen”. He has positioned anti-air missiles and other advanced missile systems in Belarus and deployed his fleet to the Black Sea in an effort to prevent a western intervention in Ukraine. The US ambassador to the United Nations responded to the news from Moscow while appearing on CBS. “President Putin is continuing to escalate this war in a manner that is totally unacceptable,” Linda Thomas-Greenfield said. “And we have to continue to condemn his actions in the strongest possible way.” At about the same time as Putin’s nuclear move, Zelenskiy’s office said on the Telegram messaging app that the two sides would meet at an unspecified location on the Belarusian border. The message did not give a precise time for the meeting. The announcement came hours after Russia announced that its delegation had flown to Belarus to await talks. Ukrainian officials initially rejected the move, saying any talks should take place elsewhere than Belarus, since it has allowed its territory to be used by Russian troops as a staging ground for the invasion. The Russian invasion has left hundreds dead. Russia has launched missile strikes against buildings in Kyiv, Kharkiv and other major Ukrainian cities as it threatens an all-out assault not seen since the second world war. Kharkiv residents were urged to stay indoors by its governor, Oleg Sinegubov, who said “there has been a breakthrough in light equipment including in the central part of the city”. A nine-storey building was reportedly hit, with one woman killed. Russian forces also blew up a gas pipeline in the city, the Ukrainian state service of special communications said, prompting the government to warn of a potential “environmental catastrophe” and to urge people to protect themselves from the smoke by covering their windows. Thousands of Ukrainian civilians, mainly women and children, were fleeing from the Russian assault into neighbouring countries. The intensification of the Russian attacks on Ukrainian cities has solidified EU resolve in confronting Moscow, with a series of unprecedented steps on Sunday. For the first time in its history, the EU will finance the purchase and delivery of weapons to a country under attack, the European Commission president, Ursula von der Leyen, said. The EU will also impose a blanket ban on Russian flights using European airspace, and on Moscow’s state-run media broadcasting in Europe. On the same day, BP announced it would be unloading its 19.75% share in the Russian oil giant, Rosneft, after holding a stake in the company for three decades. “Russia’s attack on Ukraine is an act of aggression which is having tragic consequences across the region,” Helge Lund, BP’s chairwoman said. In another dramatic step, Turkey declared it would close the straits linking the Mediterranean and the Black Sea, a power given to the country under the Montreux convention in time of war. “We came to the conclusion that the situation in Ukraine has turned into a war. We will apply the Montreux provisions transparently,” said Turkish foreign minister Mevlüt Çavuşoğlu. The convention gives Turkey the power to block the passage of Russian and Ukrainian warships, providing they are not returning to their permanent bases in the Black Sea. As all Ukrainian ships are based in Black Sea ports, the decision would only apply to the Russian navy. The EU measures come after the US, Britain and European countries announced tougher sanctions targeting Russian banks, including barring some from the Swift international payments system. In a historic announcement to the Bundestag, the German chancellor, Olaf Scholz, said a fund of €100bn (£85bn) would be set up immediately to boost the strength of the country’s armed forces, as he also announced a sustained increase in defence spending over the coming years. Scholz admitted that the urgency of the Ukraine crisis had forced Germany’s decision to invest in the military, telling the emergency session of parliament: “It is clear that we must invest significantly more in the security of our country, in order to protect our freedom and democracy.” He called it “Germany’s historical responsibility” to ensure that Vladimir Putin “does not turn the clocks back”. The move came after the government made the surprise announcement on Saturday that it would be sending weapons and other supplies to Ukraine, including 1,000 anti-tank weapons, 500 surface-to-air Stinger missiles and thousands of gallons of petrol. In another unprecedented step, the EU announced that it would finance the purchase and delivery of weapons for the first time. The European Commission president, Ursula von der Leyen, described the move as a “watershed moment”, in a speech where she also announced the EU would seek to ban Russian state-backed channels RT and Sputnik. After moves from 15 EU member states, the EU will ban Russian airlines from its airspace and announced new sanctions on the government of the Belarusian president, Alexander Lukashenko, described as “complicit in this vicious attack on Ukraine”. About 100,000 people gathered in Berlin to demonstrate against the Russian invasion of Ukraine, while from St Peter’s Square in Rome, the Pope condemned the attack, saying those who make war should not be deluded into thinking that God is on their side. As Russia’s international isolation deepened, there were growing signs of disquiet from Russia’s financial elite, following earlier protests from celebrities and sports people. The billionaire Russian businessman Mikhail Fridman, who was born in Ukraine but made his fortune in Russia after the Soviet Union collapsed, told his staff in a letter that the conflict was a tragedy for both countries. “This crisis will cost lives and damage two nations who have been brothers for hundreds of years,” he wrote in a letter seen by the Financial Times that did not criticise Putin directly. Oleg Deripaska, an oligarch and ally of the Russian president, tweeted: “Peace is the priority. Negotiations must start ASAP.”