Donald Trump accused Vladimir Putin of talking "bull****" and offering "meaningless" gestures while refusing to end his invasion of Ukraine.
The US president ramped up his criticism of his Russian counterpart on Tuesday and suggested he may be considering sanctions on Moscow.
He also vowed to send more weapons to Volodymyr Zelensky, just days after ordering a pause in weapons deliveries to Kyiv.
Mr Trump reiterated that he was "very unhappy" with Putin since their phone call last week made no progress on a peace deal, which he claimed he would settle on the first day of his second term.
Speaking to reporters during a televised cabinet meeting at the White House, Mr Trump said: "We get a lot of bull**** thrown at us by Putin, if you want to know the truth.
"He's very nice all the time, but it turns out to be meaningless."
Russian forces set a new record for the three-year conflict on Sunday with more than 500 drones and 11 missiles that wounded 26 people in the Ukrainian capital.
Last week, US officials confirmed that shipments to Ukraine of certain missiles and bombs had been suspended because of concerns about dwindling defence stockpiles.
However, Mr Trump reversed the decision in a stunning U-turn, adding: "We're going to send some more weapons.
"We have to. They have to be able to defend themselves. They're getting hit very hard now."
Mr Trump urged Pentagon chief Pete Hegseth to push defence contractors to increase production of armaments.
"We have to step them up, Pete, and let them make it at a much higher rate," Mr Trump said. "Putin is not treating human beings right. He's killing too many people.”
Asked about his interest in a Senate bill co-sponsored by Republican Lindsey Graham for further sanctions on Russia, Mr Trump responded: "I'm looking at it very strongly."
The Kremlin has yet to respond to Mr Trump's strongly worded comments about Putin.
But responding to the shipment of US weapons to Ukraine, government spokesman Dmitry Peskov said: “It is obvious that these actions probably do not align with attempts to promote a peaceful resolution.”
