While rejecting fears that Putin has already anticipated penalties being imposed by Western countries, Cleverly insisted the West’s sanctions will have “a meaningful impact”.
"This tweet will go down in the history books in the future," wrote one person on Twitter.
Washington correspondent Nomia Iqbal said the Ukrainian ambassador’s statement was "one for the history books."
Volodymyr Zelensky urged every fit military-aged Ukrainian man to take up arms and defend the country against Russia.
Brexit will be a "boon to the terror groups already active inside and outside Europe’s borders, to the Russian dictator who is crashing through those borders, and it would reduce the ability of the UK and Europe to resist these assaults."
Attacks were reported across Ukraine from around 3am, including in several western cities, close to the border with Poland.
Denouncing UK sanctions, Daria Kaleniuk said: "Putin is attacking my country, so I beg you to stand up for Ukraine."
Vladimir Putin said other countries attempts to interfere with the Russian action would result in “consequences they have never seen”.
The movement was described by organisers as a “cry for peace”.