Washington DC - President Donald Trump on Sunday accused Ukraine again of lacking "gratitude" for Washington's support against Russia's invasion, as top US and Ukrainian representatives met in Geneva for talks on a proposal to halt the war.

"UKRAINE 'LEADERSHIP' HAS EXPRESSED ZERO GRATITUDE FOR OUR EFFORTS," Trump wrote on his Truth Social platform, while also re-airing frustration at the war's "HUMAN CATASTROPHE" and attacking his predecessor Joe Biden, but offering no direct condemnation of Moscow.

Trump's blast at Ukraine and the US allies reflected the Republican's annoyance over the war, which began when Russia launched its full-scale invasion of Ukraine in 2022, seizing and destroying swaths of territory.

Trump claimed in his presidential campaign last year that he would broker a peace within 24 hours.

However, his sporadic diplomatic efforts have made little ground and he faces fierce criticism from within his own party for a new 28-point plan being discussed in Geneva that would deliver several of Russia's key war aims.

While Trump has previously said he is disappointed in Putin, he rarely criticizes the Kremlin leader directly or condemns the invasion, instead pressuring Ukrainian President Volodymyr Zelensky.

In Sunday's social media post, he criticized European countries that he said continued to buy oil from Russia and called Biden "crooked Joe" for giving Ukraine weapons "free, free, free."

The only mention of Putin in the lengthy post was to claim that the Russian president thought "Now is my chance!" to invade Ukraine only because "Sleepy Joe" Biden was in office.

Zelensky has repeatedly expressed thanks for the huge US military support to Ukraine, which continues to battle the occupying Russian forces across a front hundreds of miles long.