CAIRO, May 24 (Reuters) - Egyptian President Abdel Fattah al-Sisi agreed with U.S. President Joe Biden by phone on Friday to temporarily send humanitarian aid and fuel to the United Nations via Israel's Kerem Shalom crossing until legal mechanisms are in place to reopen the Rafah border crossing from the Palestinian side, the Egyptian presidency said. (Reporting by Mohamed Hindawy, writing by Adam Makary and Yomna Ehab)