United States President Barack Obama called Japanese Prime Minister Shinzo Abe on Sunday to offer his condolences and express his and the US's solidarity against terrorism.
Japanese hostage Haruna Yukawa is believed to have been executed by Islamic State terrorists, after a video surfaced online Saturday claiming as much.
Japan has stated that although they cannot yet confirm the video's authenticity, they fear its credibility is high.
Obama telephoned Abe from New Delhi on Sunday, after arriving to India for a three-day visit.
He called "to offer condolences for the murder…of Japanese citizen Haruna Yukawa and to convey solidarity with the Japanese people," the White House said in a statement.
"He also expressed appreciation for Japan's significant contributions of humanitarian assistance to the Middle East region. The two leaders agreed to continue their cooperation on a range of regional and global issues."
Obama joined a group of world leaders Saturday in condemning the brutal execution and calling for the release of second Japanese hostage Kenji Goto.
"The United States strongly condemns the brutal murder of Japanese citizen Haruna Yukawa by the terrorist group," he said in a statement.
"We renew our call for the immediate release of Kenji Goto and all other remaining hostages," he added. "We stand shoulder to shoulder with our ally Japan and applaud its commitment to peace and development in a region far from its shores."
AFP contributed to this report.