President Obama spoke with Ukrainian President Poroshenko this afternoon to discuss the tragic crash of flight Malaysian Airlines 17. President Poroshenko welcomed the assistance of international investigators to ensure a thorough and transparent investigation of the crash site. President Obama assured him that U.S. experts will offer all possible assistance immediately. The Presidents emphasized that all evidence from the crash site must remain in place on the territory of Ukraine until international investigators are able to examine all aspects of the tragedy.
Barack Obama, Readout of the President's Call with President Poroshenko of Ukraine Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/306263