Boris Johnson has said an attack on a kindergarten in Ukraine was a “false flag operation” by Russia which has been designed to “discredit” the Ukrainians.

       The prime minister said the picture was “grim” and warned that Moscow could launch more such operations in the coming days as a pretext for an invasion into the UK’s eastern European ally.

       “We fear very much that that is a thing we will see more of over the next few days,” Mr Johnson told reporters.

       He said: “A kindergarten was shelled in what we are taking to be – well, we know – was a false flag operation designed to discredit the Ukrainians, designed to create a pretext, a spurious provocation for Russian action.”

       Ukraine’s president Volodymyr Zelenskiy said on Thursday that pro-Russian forces had shelled a kindergarten in Donbass what he called a “big provocation”.

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       The Ukrainian military said no children were harmed, but there are reports that up to three adults suffered concussions. Kiev has accused the Russia-backed Luhansk People’s Republic (LPR) rebels of being behind the attack.

       Pro-Russia separatists claimed there had been an increase in Ukrainian shelling, describing it as a “large-scale provocation” and that they had then returned fire.

       But the Kyiv government disputed the claim, saying separatists had shelled its forces but they did not fire back.

       For its part, the Kremlin said Moscow was “seriously concerned” about reports of an escalation after the pro-Russia separatists accused the Ukrainian government forces of opening fire on their territory four times.

       Mr Johnson said he was going to the European Security Conference in Munich this weekend to discuss ways to further “unify” western allies on how to deter a Russian invasion.

       The prime minister added: “What we are doing is making that we do everything to strengthen the package of sanctions that will follow immediately should there be a Russian invasion.”

       Mr Johnson was also grilled on action to tackle “dirty” money from Russia, and whether if his government was having to rush forward the ban on Tier 1 visas used by the super-rich because of an influx in applications.

       The PM replied: “We address all the issues we can, as fast as we can. We have already some very tough laws on money laundering, on people laundering ill-gotten gains here in the UK. But, clearly, it’s time to bring in some tough sanctions against the Russian regime.”

       He said the government wanted to “stop the raising of funds by Russian companies on London financial markets – that’s a very, very tough sanction that we’ll be bringing in”.

       Home secretary Priti Patel will scrap the existing Tier 1 investor visa scheme used by oligarchs and billionaires next week, The Independent understands.

       Mr Johnson again said that the west had to end its dependency on “Russian hydrocarbons”, and again warned president Vladimir Putin to step back from war.

       “If Russia were so mad as to invade, I don’t think people should imagine that this would be a brief business,” he said. “This would be a bloody and protracted conflict in which, I’m afraid, there will be many casualties and including many Russian casualties.”

       Earlier on Thursday foreign secretary Liz Truss warned of more “false flag” operations in the coming days.

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       She said Russian reports of alleged abnormal military activity by Ukraine in Donbas were “blatant attempt by the Russian government to fabricate pretexts for invasion … This is straight out of the Kremlin playbook”.

       Ms Truss said she was “very concerned about reports today of increased Russian aggression: over 7,000 extra troops near the Ukraine border and an attack by pro-Russian troops on a kindergarten in Ukraine”.