Hardline President Mahmoud Ahmadinejad insisted Thursday that Iran is not seeking to build an atom bomb but defiantly added that should it decide to do so "no one can do a damn thing."

"When we say we do not want to make bomb it means we do not want to," Ahmadinejad was quoted by the state television website as saying.

"If we want to make a bomb we are not afraid of anyone and we are not afraid to announce it, no one can do a damn thing," he said during a ceremony inaugurating a sewage treatment plant in southern Tehran.

Iranian officials have staunchly denied Western suspicions that Tehran's nuclear enrichment programme is masking a drive for atomic weapons.

Parliamentary speaker Ali Larijani last year reiterated the denial by quoting a previous fatwa by supreme leader Ayatollah Ali Khamenei, who has the final say in the Islamic republic's affairs, which said "using weapons of mass destruction, including nuclear (arms) is haram (forbidden)."

Ahmadinejad's comments come two weeks after the chief of Iranian atomic organisation Fereydoon Abbasi Davani announced plans to triple Tehran's capacity to enrich uranium to 20 percent level in a move Washington deemed "provocative."

Despite being targeted by four sets of UN Security Council sanctions over its refusal to suspend uranium enrichment, Iran remains adamant that it will push ahead with its nuclear enrichment programme.

Enriched uranium can produce either fuel for a nuclear reactor or the fissile material for an atomic warhead. Tehran insists it will use the substance to fuel its future nuclear power plants.

Ahmadinejad also took a swipe at the UN's International Atomic Energy Agency, which has been investigating Tehran's nuclear programme for a number of years.

"They have created something called the agency and have installed a bunch of puppets," he said in an apparent reference to Western powers, adding however that Iran had nevertheless cooperated with the IAEA.

Ahmadinejad pointed to the Fukushima nuclear power plant in Japan, saying that even though the "radiation was twice as much as was said ... even then the (IAEA) kept silent."

Japan's earthquake and tsunami in March left nearly 25,000 people dead or missing, and knocked out cooling systems at the Fukushima nuclear power plant, leading reactors to overheat and triggering the worst nuclear crisis since Chernobyl 25 years ago.

Ahmadinejad dubbed the IAEA's reports on Iran as "scrap paper," adding: "I asked them why are you silent there (about Fukushima) but it is not the same when it comes to Iran."