The clashes were the worst violence since protests first erupted in the wake of the June election. Opposition protesters say the vote was rigged in favour of Mahmoud Ahmadinejad, the president of Iran, which the government denies.
"The US and Britain and other arrogant powers, as well as their domestic misguided [allies], acted under the banner of struggle against the Imam [Ayatollah Khomeini] and the revolution since the very beginning of the victory of the Islamic revolution. The situation is the same now," Khamenei said in the speech.
Khomeini, Khamenei's predecessor, came to power during the 1979 revolution and instituted the idea of clerical rule.
Rahesabz, an opposition website, said on Wednesday that more than 180 people, including 17 journalists, 10 Mousavi aides and some members of the outlawed Bahai faith, were arrested in the aftermath of the clashes.
Iran plans to try five detainees seized in connection with the Ashura day riots who it says are members of the People's Mujahideen Organisation of Iran (PMOI), an exile group opposed to Iran's Islamic system of government.
They are accused of 'moharebeh', an Islamic term meaning warring against God that carries the death penalty.
Abbas Jafari Dolatabadi, the general prosecutor of Tehran, was quoted earlier on Saturday as saying the trial of an unspecified number of Bahais, whose faith is outlawed in Iran, will start this week.