President Donald Trump said on Sunday that one of the difficulties with Russia-Ukraine negotiations is the hatred between presidents Vladimir Putin and Volodymyr Zelenskyy.

"The hatred between Zelenskyy and Putin is unfathomable," he said, adding "they're incapable of talking to each other."

Trump also called on NATO allies to boost economic pressure on Russia to try to end the war.

And he said some NATO nations are indirectly buying oil from Russia.

"Countries are buying oil from Russia and selling it into certain NATO countries. Not all. But certain very substantial NATO countries," he said.