U.S. President Donald Trump once more appears to be losing patience with Vladimir Putin's warfare in Ukraine, but it remains unclear whether he will actually toughen his stand against the Kremlin leader.

The Republican billionaire, who returned to office in January vowing to end the war "in 24 hours," has long appeared to side with his Russian counterpart, frequently speaking of him with gushing admiration.

Volodymyr Zelenskyy, meanwhile, has been a frequent target of Trump's ire, as seen with the spectacular dressing down of the Ukrainian leader in a tense Oval Office meeting in March.