WASHINGTON (Reuters) - U.S. President Barack Obama and Ukraine President Petro Poroshenko emphasized in a phone call on Thursday that all evidence from the downed Malaysian jetliner must remain in Ukraine for investigators to see.

"President Poroshenko welcomed the assistance of international investigators to ensure a thorough and transparent investigation of the crash site," the White House said of the call. "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," it said.


(Reporting by Jeff Mason; Editing by Bill Trott)