Washington DC - President Donald Trump said Wednesday Xi Jinping could have a "big influence" on Russia's Vladimir Putin over efforts to end the war in Ukraine, days ahead of a meeting scheduled between the US and Chinese leaders in South Korea.

"I think he can have a big influence on Putin... Look, he's a respected man. He's a very strong leader, very big country. Yeah, I think it can have a big influence. And we will certainly be talking about Russia, Ukraine," Trump told reporters at the White House.

Trump has counted on personal chemistry with Putin to reach a Ukraine peace deal, but has found himself frustrated time and again by the Russian leader.

The US president expressed irritation with Putin on Wednesday, telling journalists: "Every time I speak with Vladimir, I have good conversations, and then they don't go anywhere."

Trump was due to meet Putin in Hungary within weeks, but on Tuesday scrapped the summit, saying he did not want to have a "wasted meeting."

The US leader is trying to end Moscow's more than three-and-a-half-year full-scale invasion of its neighbor through talks with Ukraine's Volodymyr Zelensky and Russia's Putin.

But while Trump has upended a years-long Western policy of isolating the Russian leader, he has made little concrete progress toward a peace deal so far.