TEHRAN: Tens of thousands of demonstrators are gathering outside the former US Embassy in Iran for the biggest anti-American rally in years as a show of support for hard-line opponents of President Hassan Rouhani's historic outreach to Washington.

Such protests occur every year outside the former embassy compound to mark the anniversary of its 1979 takeover following the Islamic Revolution. A total of 52 hostages were held 444 days.

But Monday's rally is the largest in years after calls by groups such as the Revolutionary Guard for a major showing, including chants of ''death to America'' that some of Rouhani's backers have urged halted.

Rouhani's overtures are backed by Iran's Supreme Leader Ayatollah Ali Khamenei. Opponents, however, say they will not back down, raising the prospect of deeper internal rifts.