A leading Iranian reformer accused hardliners of a "fascist or totalitarian" approach, as President Mahmoud Ahmadinejad's new cabinet prepared to hold its first meeting on Sunday after his disputed re-election in June, Reuters reported.
The hard-hitting comment by former President Mohammad Khatami was a further sign of the moderate opposition's intention to keep up protests over an election it says was rigged.
It came three days after parliament approved most of Ahmadinejad's government ministers in a move that bolstered his position after nearly three months of political turmoil in the world's fifth-largest oil exporter.
The reshuffled government was due to meet for the first time on Sunday evening in the northeastern city of Mashhad, site of Shi'ite Iran's holiest shrine.
The presidential poll, which was followed by huge opposition demonstrations, plunged Iran into its deepest internal crisis since the 1979 Islamic revolution and exposed deepening rifts within its ruling clerical and political elites.
The authorities reject charges the vote was fraudulent.
"We believe they destroyed in this election the biggest opportunity that had come about for the Islamic establishment and the country," Khatami said in a meeting with university professors in Tehran, the ILNA news agency reported.
He said: "We are opposed to the interpretation of religion by those who in the name of confronting Western liberalism want to drive people by force on to the path they regard as prosperous using a fascist or totalitarian approach."
The authorities have portrayed the opposition protests as a foreign-backed bid to undermine the Islamic state's leadership. Last month, Iran began mass trials of senior reformist figures it accuses of fomenting the unrest, including Khatami allies.
The elite Revolutionary Guards and a pro-government Islamic militia put down the post-election street protests. The opposition says 72 people were killed in the violence, nearly three times the official estimate.
IRAN'S "PACKAGE"
Khatami said the election had been an "opportunity to have the youth and people who were dissatisfied ... to return to the scene and make the right choice with hope in the establishment and the future."
Khatami, who was president in 1997-2005, backed opposition leader Mirhossein Mousavi in the vote. The Guards have called for both of them to be put on trial.
Another leading reformist criticised the cancellation of an annual religious ceremony where Khatami had been due to speak and which could have become a rallying point for moderates.
Iranian media said the Sept 9-11 event was called off after the authorities put pressure on its hosts.
"The cancellation of the ceremonies at Imam Khomeini's shrine will hurt the prestige of the Islamic Republic," said Mohammad Salamati, head of the moderate Islamic Revolution Mujahideen Organisation party, ILNA reported.
Ahmadinejad's new government includes the Islamic state's first female minister, and a military commander as defence minister who Argentina accuses of involvement in a 1994 attack on a Buenos Aires Jewish centre which killed 85 people.
Iran has repeatedly denied any link to the bombing.
"After almost 15 years they have not been able to present a single evidence proving Iran's involvement," Mehr News Agency quoted Foreign Ministry spokesman Hassan Qashqavi as saying.
The June election added to tension between Iran and Western powers, already at odds over Tehran's nuclear programme, after Iranian officials accused them of backing the protesters.
U.S. President Barack Obama has given Iran until later in September to take up a six powers' offer of talks on trade if it shelves nuclear enrichment or face harsher punitive measures.
Iranian officials say Tehran will soon present its own "package" of proposals to the big powers, without making clear to what extent it addresses the nuclear row.
The West suspects Iran of trying to build nuclear bombs. Iran says its programme is for peaceful power generation and has repeatedly rejected demands to halt sensitive atomic activity.
Israel and the United States have not ruled out possible military action if diplomatic efforts fail to resolve the row.
Iran said on Sunday it had a developed a weapons systems to intercept incoming cruise missiles, state-run Press TV reported.
"Today, the military is able to both detect stealth cruise missiles and destroy them," it quoted General Ahmad Miqani, an air defence commander, as saying.