The Ayatollah was a key figure in the rise of political Islam
Ayatollah Ali Khamenei, Iran's supreme leader, has strongly criticised the US as Iran marks 20 years since the death of the founder of the Islamic republic.
He said the US remained "deeply hated" in the region and "beautiful and sweet" words would not change that.
He told the huge crowd at the mausoleum of his predecessor, Ayatollah Khomenei, that action was needed not words.
He also demanded calmer exchanges between presidential candidates after a fiery televised debate on Wednesday.
Incumbent President Mahmoud Ahmadinejad accused his rivals of corruption, while his leading opponent, Mir-Hossein Mousavi, said Mr Ahmadinejad's foreign policy was undermining the dignity of the Iranian nation.
From Jon Leyne, BBC Tehran correspondent
After 20 years, the figure of Ayatollah Khomeini still dominates. His picture is on display in every public building and the system he created lives on, much as he designed it.
Even critics of Ayatollah Khomeini would accept that his was a huge, charismatic, presence, not that criticism of him is advisable inside Iran.
He was an astute administrator and a very able politician with a degree of ruthlessness. He has been widely demonised in the West, but this man, so little understood outside Iran, is one of the key figures in the rise of political Islam, a movement that is one of the most powerful forces in the world today.
Mr Khamenei warned candidates that they should not let their differences of opinion lead to chaos.
The ayatollah's speech came just hours before US President Barack Obama was to deliver a speech in Cairo aimed at establishing a new relationship with the Muslim world after years of tense relations under the Bush administration.
"In the past few years, American governments, especially the government of the foolish former president... have occupied two Islamic countries, Iraq and Afghanistan, under the pretext of the fight against terrorism," he said.
"You witness that in Afghanistan, American warplanes bomb people and kill some 150 not once, but 10 and 100 times. They kill people continually. So, terrorist groups, do what you are doing there," he added.
"If the new president of America wants a change of face, America should change this behaviour. Words and talk will not result in change."
Mr Khamenei went on to urge candidates in next week's presidential election to avoid damaging each other's reputation and to work towards a common purpose.
He also accused foreigners of trying to discredit the elections, with "foreign radio programmes tarnishing the elections, making people pessimistic".
Under Iran's Islamic revolutionary system, designed primarily by the late Ayatollah Khomenei, the president is elected by universal suffrage, but it is the supreme leader who is empowered to determine all the key decisions of the state.