Kyiv - Prince Harry, the younger son of Britain's King Charles, made an unannounced visit to Ukraine on Thursday to show his support for the country, which he said is "bravely and successfully defending Europe's eastern flank."

During an address at the Kyiv Security Forum on Thursday morning, Harry contrasted European support for Ukraine with the United States. 

"The United States has a singular role in this story not only because of its power but because when Ukraine gave up nuclear weapons, America was part of the assurance that Ukraine's sovereignty and borders would be respected," he said. "This is a moment for American leadership, a moment for America to show that it can honor its international treaty obligations, not out of charity but out of its own enduring role in global security and strategic stability."

Harry said Europe's support has been crucial to Ukraine's defense but that more is needed faster. 

"Europe has stood up in profound ways. And that support has mattered, and Ukraine knows it," Harry said. "The task now is to match endurance with speed."

Harry described the war as an ideological battle between liberal democracies and their authoritarian foes. 

Pointing to the forcible deportations of tens of thousands of Ukrainian children to Russia, Harry said that the "distinction could not be clearer" between Ukraine's respect for international law and human life and Russia's lack of it. 

"Under international law, this forcible transfer of children from one national group to another is not just a war crime. It can constitute an act of genocide. When carried out with intent to destroy a people's identity," he said.