Iran's controversial nuclear programme has for years been a point of contention between the Islamic republic and the P5+1 countries, the United States, Britain, France, China, Russia and Germany, who suspect the drive is aimed at developing atomic weapons.
"We have announced repeatedly that we are against developing nuclear bombs," said the 67-year-old presidential candidate, in an exclusive interview with AFP, who, along with seven others, has been approved by the hardline electoral watchdog the Guardians Council to run in the June 14 presidential poll.
"Our supreme leader says developing a bomb is religiously forbidden," said Velayati, referring to a much-debated religious decree against nuclear weapons issued by Khamenei.
World powers have slapped sanctions on Iran but have so far failed to convince it to cut back on its nuclear drive, while parallel efforts by the UN's International Atomic Energy Agency to shed some light on Iran's past activities have failed.
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"We have tried to respond to all the questions they have raised in more than 10 years," said Velayati.
On Sunday, French President Francois Hollande echoed Western concerns about the Iranian nuclear drive, saying there was an "urgent and imperative need to prevent Iran from obtaining nuclear weapons."
Velayati condemned Hollande's call as "slogans" that have been repeated over and over again.
"What they say does not help to solve the nuclear issue," he said.
Israel, the sole but undeclared owner of nuclear bombs in the Middle East, has not ruled out military attacks against its arch-foe Iran to stop it getting closer to the bomb, neither has US President Barack Obama.