Iran's hard-line President Mahmoud Ahmadinejad on Monday blasted critics of his nuclear policies as "traitors" and accused them of spying for Iran's enemies, using his strongest rhetoric yet against domestic opponents and raising concerns of a possible crackdown.

Ahmadinejad's tough comments appeared to be an escalation aimed at silencing calls for him to compromise with the West over Iran's nuclear program, at a time of increasingly high-level criticism of his policies within the country's ruling establishment.

Ahmadinejad has moved to exert greater control over the nuclear issue, replacing Iran's top nuclear negotiator, Ali Larijani, with a close loyalist -- a step that angered even some conservative politicians.

At the same time, complaints against the president have become more vocal. Ahmadinejad has long faced domestic criticism that he was failing to improve the worsening economy and has needlessly worsened the stand-off with the West with his inflammatory speeches.

But recently, more leading figures have spoken out. Last month, Larijani's predecessor as top nuclear negotiator, Hasan Rowhani, delivered an unusually sharp rebuke to Ahmadinejad, saying he was making more enemies for Iran with his policies.

One of Iran's most powerful cleric-politicians, former president Ayatollah Akbar Hashemi Rasfanjani, issued a veiled criticism of Ahmadinejad last week, saying officials must "avoid immaturity and not cause trouble for the people."

On Monday, Ahmadinejad warned he would expose his critics, saying, "They are traitors."

"If internal elements do not stop pressures concerning the nuclear issue, they will be exposed to the Iranian nation," Ahmadinejad said in a speech to students at Tehran's Science and Industry University in Tehran. "We have made promises to the people and believe anyone giving up over the nuclear issue is a traitor."

He accused critics of regularly providing "the enemy" with "information from within the ruling system."

"We even have a recorded speech of one of them who tells the enemy, 'Why should you give up? ... Step up pressures to make them (Iran) retreat,"' Ahmadinejad said, without identifying the person he was referring to, according to the state television Web site.

The president said one official has already been arrested for espionage and accused his critics of pressuring the courts to acquit him. "But I announce here that the Iranian nation won't allow these persons and groups to use political and economic influence to save criminals from the clutches of justice," he said.

Ahmadinejad did not name the official. But earlier this year, Hossein Mousavian -- an ally of Rafsanjani who was the top nuclear negotiator under former reformist President Mohammad Khatami -- was briefly detained. Authorities have not said what charges he faces, but the semiofficial Fars news agency has reported that the charges were likely related to espionage.

Rafsanjani, who lost to Ahmadinejad in 2005 elections, has emerged as the leader of Iran's camp of moderate conservatives, many of whom were former supporters of Ahmadinejad who have since become disillusioned with his rule. The camp is likely the most worrisome domestic challenge for Ahmadinejad, since -- unlike more liberal reformists -- they have influence with Iran's supreme leader, Ayatollah Ali Khamenei.

Rafsanjani on Monday warned that Iran was facing "serious threats."

"We are subject to big conspiracies. Regional tensions are at its peak. Americans have deployed their forces everywhere they wanted. There is danger. It is serious," Rafsanjani said in a speech at a Tehran conference, with Rowhani and Mousavian sitting next to him. It was Mousavian's first major public appearance after being released in May.

Reformist lawmaker, Esmaeil Gerami Moghadam, said Ahmadinejad's harsh comments were "the beginning of a new crackdown against his critics. He is resorting to threats to escape plausible criticism."

Mohammad Ravanbakhsh, a reformist writer, said Ahmadinejad denounces anybody opposing his policies as being weak or being an agent of the enemy.

"Ahmadinejad assumes that anybody opposing his policies is either a compromiser giving in to the West or is a coward," he said.

The United States and some of its allies accuse Iran of seeking to develop nuclear weapons, a claim denied by Iran, which says its program aims only to generate electricity. Iran has taken a tough stance, rejecting United Nation's demands that it suspend uranium enrichment, a process that can produce either fuel for a reactor or a nuclear warhead.

On Monday, Ahmadinejad again insisted that there will be no halt or slowing down of Iran's uranium enrichment.

"Today, bad-wishers ... try to get a very small concession from this nation. In the latest talks, they raised the issue of declining the installation of centrifuges ... we don't accept this," he said.