Demonstrators in Tehran today chanted traditional slogans against the US and Israel at a time when new US President Donald Trump has already engaged in a war of words with Iran's leadership and put Tehran "on notice" over a recent ballistic missile test.
Among other places, demonstrators marched toward Azadi Square, where President Hassan Rouhani will address the crowd. State television aired footage of commemorations in Tehran and other cities and towns across the country, many of them in subzero weather.
The rallies commemorate February 11, 1979, when followers of Ayatollah Ruhollah Khomeini ousted the US-backed Shah Reza Pahlavi.