The US president will speak to Ukraine's leader in a call on Wednesday, two days before "one-to-one" talks with Putin.

American officials quickly discovered a major snag in planning for the summit: summertime is peak tourist season in Alaska, and options both available and equipped to host the two world leaders were severely limited.

Russia says it invaded Ukraine to halt Kyiv's ambitions to join NATO, the U.S.-led defensive alliance, which it saw as a major security threat. It also accuses Kyiv of persecuting ethnic Russians and their culture in Ukraine.