"This is a nauseating masquerade that the Zionists and Americans organized and bought a ticket for, and for which they are the only spectators. The Iranian nation has seen a lot of such masquerades," Ahmadinejad added.
It was the first public speech the president had given since the eruption of reformist protests in his country a few days ago, which have so far claimed the lives of at least 15 people. At least 20 have been arrested.
The nephew of opposition leader Mir Hossein Mousavi was one of the victims of the protests, and the conservative Kayhan paper ran an editorial blaming Mousavi for his death. The editor, Hossein Shariat Madari, also claimed that the opposition leader had ties with "Zionists" and received orders from the Israeli Mossad.
"Since the beginning of the riots all evidence shows that there is a connection between the leaders of the struggle to the Zionists and that they have received orders directly from the Mossad and the CIA," wrote Madari, who is known as an associate of Supreme Leader Ayatollah Ali Khamenei.
"The barbaric and bloodthirsty enemies and the agents who accept orders from Israel did not even refuse to plan the murder of their own nephew," he added.
'Assasination plot'IRNA reported on Monday that Ali Mousavi's body had been removed from the hospital in which it had been kept along with four others in order to complete the inquest into their deaths.
Expelled Iranian film director Mohsen Makhmalbaf, who is affiliated with the reformist movement, claimed Monday that a number of men who had come to assassinate Mousavi shot him from close range.
"The type of bullet, the type of weapon, and the rest of the existing evidence prove that this was without a doubt an assassination plot," IRNA quoted him as saying.
Makhmalbaf said the assassination was a ploy to put pressure on Moussavi, but the assassins' identity and that of those who sent them remain unclear.
Also Tuesday, Iran's Revolutionary Guards said the Western media was conducting "psychological warfare with the aim of toppling the ayatollah regime". The reformists, on their part, called on the leaders of Iran to honor its constitution and apologize to the nations for the violent occurrences.
Reuters contributed to this report