Handshake for Obama and Raúl Castro of Cuba

President Obama and President Raúl Castro of Cuba shook hands here on Friday night, and American officials said they would hold discussions on Saturday during a gathering of regional leaders, in the first full-fledged meeting between presidents of the United States and Cuba in more than a half-century.

The expected encounter was not on Mr. Obama’s official schedule, but it held deep significance for the regional meeting, as the president’s move to ease tensions with Cuba has overshadowed the official agenda.

Mr. Obama is nearing a decision on removing Cuba’s three-decade-old designation as a state sponsor of terrorism, citing progress in the effort to re-establish diplomatic ties after half a century of hostilities.