US President Donald Trump lashed out Sunday at the leaders of both warring parties in Russia's invasion of Ukraine, expressing frustration as efforts to kick-start ceasefire talks remain deadlocked.

Trump first criticised Russian President Vladimir Putin for questioning the credibility of Ukraine's Volodymyr Zelensky as a negotiating partner, saying he was "very angry, pissed off" with the Kremlin chief.

But the US leader later softened his tone on Putin and instead turned his ire on Zelensky, warning him Ukraine would have "big, big problems" if he got cold feet over a deal to sign over mineral rights to the United States.

Trump is trying to broker a ceasefire between Ukraine and its Russian invader, and has been pushing Zelensky to sign an agreement to give US firms exclusive access to Ukrainian rare earth minerals.

Earlier Sunday, NBC News journalist Kristen Welker said Trump had called her to express his fury over Putin questioning Zelensky's future -- something Trump himself has done -- and threatening secondary tariffs on firms dealing........

© International Business Times