Iran’s supreme leader vowed Wednesday to press ahead with the country’s nuclear energy program, while also reiterating his denials of any intention to produce nuclear weapons.

Addressing a group of nuclear scientists, Ayatollah Ali Khamenei said: “The Islamic Republic of Iran, with a thoughtful, jurisprudent, theoretical approach, believes that owning a nuclear weapon is a big sin. It also believes that keeping such a weapon is vain, harmful and dangerous.”

He insisted that Iran’s enemies know it does not seek nuclear weapons but want to prevent the country from making scientific advances to preserve their dominance. “Pressure, sanctions and assassinations will only help the Iranian people realize that they are on the right path and they will continue” on this path, Khamenei said. “If nations can make independent progress in nuclear, aerospace, technological, scientific and industrial fields, there won’t remain any more ground for the world powers to continue their bullying hegemony.”

Khamenei made the remarks after the International Atomic Energy Agency announced that a delegation had failed to make progress in clearing up allegations about Iran’s pursuit of nuclear weapons technology. The supreme leader made no mention of the IAEA team, which was barred from visiting a key military testing facility about 18 miles southeast of Tehran.

The U.N. nuclear watchdog’s mission to Iran coincided with a surge of bellicose rhetoric that some analysts said signaled a shift from a defensive posture to threats of preemptive action.

“We do not wait for the enemies to strike us,” Mohammad Hejazi, a general in charge of logistics and industrial research, told the semiofficial Fars News Agency on Tuesday. He cited a strategy that Fars said Khamenei laid out in November, warning of a tough response to any attack or threat against Iran.

“Iran is not a nation to sit still and just observe threats from fragile materialist powers which are being eaten by worms from inside,” Fars quoted Khamenei as telling military college students. “Iran will respond with full force to any aggression or even threats in a way that it will demolish the aggressors from within.”