Iran’s supreme leader signaled Friday that Tehran would crack down hard on protesters who have demonstrated against the theocratic regime for nearly two weeks after dramatic images showed riots breaking out across the country Thursday night. Ayatollah Ali Khamenei, 86, condemned what he called “a bunch of rioters [who] destroyed a public building just to please the president of the United States.” “Iranians must maintain their unity,” added Khamenei in remarks aired on state television to an audience chanting “Death to America!”