Obama also announced that $5 million in night-vision goggles, body armor and telecommunications equipment for the Ukrainian military would be delivered. He is on a four-day trip to Europe, and Warsaw was his first stop.
Poroshenko was elected Ukrainian president on May 25, and will be inaugurated on June 7.
American officials have emerged from their first dealings with Poroshenko -- a billionaire committed to integrating Ukraine into Europe and away from the Russian sphere of influence -- hopeful he can overhaul a corrupt and dysfunctional political system. He has also dealt with Russian President Vladimir Putin, who has said Russia would recognize the outcome of the vote that installed Poroshenko in the presidency.
The U.S. has made it clear that helping make Ukraine stronger economically, and helping curtail its reliance on Russia for energy, is the best way to ensure its success.
Poroshenko was seen talking at length Tuesday evening with U.S. Secretary of State John Kerry at a banquet sponsored by the Polish government in Obama's honor. Kerry and Poroshenko spoke again on Wednesday, before Kerry traveled to Paris for meetings with Russian Foreign Minister Sergey Lavrov.
Meanwhile, U.S. Vice President Joe Biden is expected to attend Poroshenko's inauguration.