Pakistan, July 5 -- Hundreds of thousands of mourners began a dayslong funeral Saturday for Iran's late Supreme Leader Ayatollah Ali Khamenei, beating their chests in sorrow before the glass case containing his flag-draped coffin in Tehran and calling for revenge against Israel and the United States.

The funeral for Khamenei, who ruled Iran for decades before being killed at age 86 in a Feb. 28 airstrike in the opening moments of the Iran war, could provide a boost for the country's theocracy and its new supreme leader, his son Ayatollah Mojtaba Khamenei.

That is particularly important as Iran tries to leverage its hold on the Strait of Hormuz in negotiations with the U.S. over a permanent end to the war and as concern still lingers tha...