That was a chant of Iranian regime thugs as they broke up an unauthorized demonstration by “Mothers of Iran for Peace” in Tehran against Israel’s military operation in Gaza. (Better not to think what would have happened to them had they been demonstrating in support of Israel.)
Azarmehr also links to a video of someone in Iran leading rather half-hearted chants of “Death to Israel” and “Death to America,” only to accidentally (?) chant “Death to Palestine”– much to the amusement of the crowd.
How long before they latch onto the old Fascist slogan from the Spanish Civil War: ¡Viva la muerte!