Thousands of Iranians gathered at the mausoleum of the Islamic republic's founder Ayatollah Ruhollah Khomeini in Tehran on Friday to launch celebrations for the 40th anniversary of its revolution.
The ceremonies for the 1979 revolution started at 9:33 am (0603 GMT), the exact time that Khomeini returned to Iran and his plane touched down at Tehran airport, AFP correspondents said.
As an army band played revolutionary anthems, the huge hall of the mausoleum was filled with people from all walks of life, amid schoolchildren dressed in the red, white and green of the Iranian flag.
Ayatollah Ahmad Jannati, head of the influential experts assembly which appoints the supreme leader of the Islamic republic, delivered a keynote speech rebuking factions seeking better ties with Washington.
"Curses on the wrong school of thought that thinks we can't run the country unless America helps us," he said, shaking a raised left hand.
"America's power is on the decline, we should not be afraid of America," Jannati said.
On February 1 each year, Iran begins 10 days of celebrations to mark the anniversary of Khomeini's return from exile after the pro-Western shah fled Iran following widespread demonstrations.
The celebrations culminate on 11 February which marks the fall of 2,500 years of monarchy in Iran.