On February 11, 1979, Iran's army declared its neutrality, paving the way for the collapse of the US-backed monarch, the United States' closest ally in the Middle East
Hundreds of thousands of Iranians held nation-wide rallies on Monday to mark the 40th anniversary of the fall of the Shah and the triumph of Ayatollah Ruhollah Khomeini, the Shia cleric who led an Islamic Revolution that rattles the West to this day.
On February 11, 1979, Iran's army declared its neutrality, paving the way for the collapse of the US-backed monarch, the United States' closest ally in the Middle East.
State TV showed large crowds defying frigid weather and carrying Iranian flags while chanting "Death to Israel, Death to America," trademark chants of the revolution which toppled the United States' most important ally in the Middle East.
One banner read: "Much to the dismay of America, the revolution has reached its 40th year."
The large turnout in state-sponsored rallies came as Iranians face rising prices, food shortages and high inflation that have triggered waves of protests.
US President Donald Trump pulled out of Iran's 2015 nuclear deal with world powers last year and re-imposed sanctions on Tehran, dealing a blow to the country's economy. Iranian officials said the move amounted to "economic warfare"
In a speech at Tehran's Azadi (Freedom) square, President Hassan Rouhani dismissed US efforts to isolate Iran, saying US sanctions could not break the Islamic Republic.
"We will not let America become victorious… Iranian people have and will have some economic difficulties but we will overcome the problems by helping each other," he said in a speech.
Iran was determined to expand its military power and ballistic missile programme despite mounting pressure from hostile countries to curb Iran's defensive work, state TV reported Rouhani as saying.
Soldiers, students, clerics and black-clad women holding small children flocked to the streets of cities and towns, many carrying portraits of Khomeini and Iran's current Supreme Leader Ayatollah Ali Khamenei.
Regional power Saudi Arabia and other Arab countries have viewed Iran with great suspicion since the Islamic Revolution swept the Shah from power, fearing Khomeini would inspire Islamic militants across the region.
Iran and Saudi Arabia are locked in proxy wars in Iraq, Yemen and Syria.