Billionaire mogul and White House frontrunner Donald Trump accused US President Barack Obama on Friday of paying "lip service" on Ukraine and failing to stand up to Russian strongman Vladimir Putin.
"Our president is not strong, and he is not doing what he should be doing for the Ukraine," the outspoken Republican Party candidate told an international conference in the Ukrainian capital via video link.
"It's lip service and nothing else," he said to a scattering of applause from an audience comprised of several hundred foreign investors and diplomats.
Trump's blunt style and charisma has made him a rock star in the eyes of Republican voters who accuse other candidates of being political insiders who refuse to speak honestly on vital issues and revert to prepared talking points.
But he has also been accused of failing to give details of how he intends to solve America's foreign policy and economic problems that particularly worry many Americans.
Trump told the Kiev audience that Obama had failed to show strength in the face of an increasingly nationalistic and diplomatically-aggressive Putin.
"Part of the problem that the Ukraine has with the United States is that Putin does not respect our president whatsoever," said the property tycoon.
Trump failed to specify whether he backed providing military assistance to the former Soviet country against what it views as Russia's "aggression" in its separatist east.
Obama has refused to ship offensive weapons to Kiev out of concern it may further anger Putin and escalate Ukraine's 17-month war.
Russia denies any links to the insurgents and officially provides them only with political backing at negotiations and UN Security Council forums.
The United Nations estimates that the violence has killed nearly 8,000 people -- most of them civilians -- since April 2014.