Iranians are marking 24 years since the death of the founder of the Islamic Republic, Ruhollah Ayatollah Khomeini.
The commemoration on Tuesday at his shrine in Tehran was attended by Supreme leader Ayatollah Ali Khamenei, President Mahmoud Ahmadinejad, along with other high-ranking officials and clerics.
Hassan Khomeini, the grandson of the late Ayatollah, was due to address the crowd later in the day.
The commemoration comes 10 days before crucial presidential elections.
Khomeini is seen as the man who led the country's Islamic revolution 34 years ago. After spending 15 years in exile, Khomeini returned to Tehran in 1979 to overthrow the US -backed Shah.
Al Jazeera’s Soraya Lennie, reporting from the Iranian capital, said Ahmadinejad did not address the crowd in the commemoration, an event at which he had spoken in previous years.
"It was a rather awkward encounter for the president. He looked very uncomfortable as he sat there in Imam Khomeini’s shrine," Lennie said.
She said that reflected the growing tension between the presidency and the country's religious establishment.
"He was seated next to the grandson of Khomeini, who is very influential here. The two men had a famous falling out four years ago when Hassan Khomeini backed the reformist candidates in the presidential elections," Lennie said.
In a televised speech to mark the anniversary, Khamenei urged presidential candidates not to make concessions to the West.
His remarks followed statements by some of the eight candidates that they would focus on improving Iran's relations with other countries.
"Some, following this incorrect analysis - that we should make concession to the enemies to reduce their anger - have put their interests before the interests of the Iranian nation. This is wrong,'' he said.
On Monday, the US announced new sanctions against Iran, directly targeting the rial currency for the first time and also the car-making sector, an important source of jobs and revenue.
The measures, which could wreak more economic deprivation inside Iran, followed Tehran's refusal to cede ground in stalled world power talks on its nuclear programme.
They were accompanied by new US warnings of a "painful" and "powerful" escalation of sanctions, as President Barack Obama seeks to convince the Islamic Republic that the price of uranium enrichment is too high.