Washington - President Barack Obama called Ukraine's president-elect Petro Poroshenko on Tuesday and offered him "the full support of the United States".
Obama said the United States would assist Ukraine as Poroshenko "seeks to unify and move his country forward," the White House said.
Poroshenko, a billionaire tycoon, won with 54% of the votes cast in Sunday's elections in the strife-torn former Soviet republic.
Obama "stressed the importance of quickly implementing the reforms necessary for Ukraine to bring the country together and to develop a sustainable economy, attractive investment climate, and transparent and accountable government that is responsive to the concerns and aspirations of all Ukrainians," the White House said.
"The two leaders agreed to continue their conversation during the president's upcoming trip to Europe," it added.
Obama is scheduled to travel to Europe in early June for the commemorations of the 70th anniversary of the D-Day landings in Normandy.
Russia, which annexed Crimea and has sided with pro-Russian militants in eastern Ukraine, has said a visit by Poroshenko to Moscow was not envisioned.
The Ukrainian military, meanwhile, claimed to have re-established control of the airport in Donetsk in eastern Ukraine, after fighting that left 40 dead. The OSCE said it had lost contact with four of its observer.