As reported by Censor.NET, this was announced by president's press secretary Sviatoslav Tseholko on his Facebook page.
"President Obama reiterated support for Ukraine as well as efforts by President Petro Poroshenko aimed to protect the territorial integrity and sovereignty of Ukraine," he wrote.
Tseholko noted that during the conversation, the US president stressed that the United States will continue supporting Ukraine which implements reforms and proceeds seeking a diplomatic settlement of the conflict.