Thousands of young Iranians have marched in the capital Tehran in honour of "national anti-global arrogance day" on 4 November.
Demonstrators converged around the former US embassy in Tehran
The rally was held two days early because Friday is likely to coincide with Eid al-Fitr, the end the holy month of Ramadan, in Iran.
Demonstrators converged around the former US embassy in Tehran to mark the 26th anniversary of its takeover.
Later, a bomb exploded near the offices of two British companies.
The bomb attack and demonstration come as Iran becomes increasingly exasperated with Western criticism of its government and nuclear programme.
The slogan for the event was "peaceful nuclear energy is our legitimate right".
Protestors gathered outside the former US embassy - the so-called "den of spies" - in memory of the day when Iranian revolutionaries seized it.
Islamic militants took 52 American hostages inside the embassy on 4 November 1979 to demand the extradition of the Shah, in the US at the time for medical treatment, to face trial in Iran.
The American hostages were eventually released on 20 January 1981, ending 444 days in captivity.
According to the official Irna news agency, Iranians also use the anniversary to disavow global arrogance and to renew their allegiance to the ideals of the Islamic revolution, the late Imam Khomeini, the founder of the Islamic republic, and Ayatollah Khamenei, the current supreme leader.
Only hours after the march began, a small explosive device went off near the offices of two British companies based in Tehran.
The bomb exploded on the 10th floor of a building where British Airways and British Petroleum are based, the British embassy told the BBC.
A couple of windows were damaged, but nobody was injured.
There was a similar attack on the same floor in August, which also did not injure anyone.
The BBC's correspondent in Tehran, Frances Harrison, says that the blasts seem designed to send a message that frustration with Britain is rising.
Recent weeks have seen Iranian officials accusing Britain of being behind a series of bomb blasts in the south-west of the country near the Iraqi border, and there has been tension because of Britain's role in confronting Iran over its nuclear programme.