As Mr Witkoff returned home, Moscow launched 21 ballistic missiles at Kyiv in three waves of attacks, Mr Zelensky said on Thursday.
Earlier, No10 suggested the Government was wholly at odds with Mr Witkoff’s description of Mr Putin.
A Downing Street spokeswoman said: “We certainly do not recognise that characterisation, and President Putin has killed thousands of people, both innocent Ukrainians and his own Russian people, who he has sent to their deaths on the frontline.
“He is starving children and the elderly of the heat and warmth, and systematically targeting critical national infrastructure.
“Ukraine’s foreign minister summed it up well this morning when he said: ‘This night, the residents of Kyiv heard what Russian humanitarianism really sounds like’.”
Asked whether the Government would make the same argument directly to the US administration, the spokeswoman added: “We engage regularly at a range of levels with a range of partners on Ukraine, and I’m sure we will continue to do so.”