Senator Bernie Sanders has urged his supporters that his Democratic rival, Hillary Clinton, "must become the next president."

Sanders spoke to delegates at the opening session of the Democratic National Convention last night.

Earlier in the day, Sanders drew jeers when he spoke to supporters, but the crowd on that evening cheered so long and loud that it took him several attempts to begin his speech.

For months, Sanders, 74, mounted an unexpectedly tough challenge to Clinton, 68, a former secretary of state, who this week will become the first woman nominated for president by a major U.S. political party.

Democratic officials have been eager to provide a show of unity at the convention, and Sanders obliged, telling sometimes-tearful supporters that he "stands with" Clinton, but that the political revolution they worked for will continue.