Iran has no intention of developing nuclear weapons, but if it wanted to the United States could not thwart it, supreme leader Ayatollah Ali Khamenei said on Saturday.
"We believe nuclear weapons must be abolished and we have no intention of building" such weaponry, Khamenei said in remarks posted on his website leader.ir.
But, Khamenei said, "if Iran had such intentions, the US could in no way prevent it" from making an atomic bomb.
The West and Israel suspect the Islamic republic is masking the development of an atomic weapons capability under the guise of a nuclear programme that Iran insists is purely peaceful.
US President Barack Obama on Tuesday urged Tehran to "recognise that now is the time for a diplomatic solution" to the nuclear stand-off.
"And we will do what is necessary to prevent them from getting a nuclear weapon," Obama said.
Khamenei's remarks come less than two weeks before a major meeting in Almaty on February 26 between Iran and six world powers -- the United States, China, Russia, Britain, France and Germany -- seeking to curb its nuclear activities.
Decisions about the disputed nuclear drive rest with Khamenei, who has declared possession of atomic weapons a "sin" banned by religion.
On Saturday, Khamenei repeated that claim and said Iran's stance on weapons of mass destruction was not taken "because the US is unhappy, but because it is based on a religious belief that nuclear weapons are a crime against humanity."
He accused Washington of "deceit" in its approach towards the Iranian nuclear drive, saying: "They want to keep us from our legitimate rights of uranium enrichment and peaceful use of nuclear energy."
Provocative declarations on what Iran considers as a non-negotiable "right" to pursue a nuclear energy programme are not unprecedented.
President Mahmoud Ahmadinejad has said in 2012 that if Iran wanted to build the bomb, "it would not be afraid to announce" its decision to the world.
Tehran has spurned UN Security Council demands to abandon its uranium enrichment programme, a process that can be used for peaceful atomic purposes as well to make the core of a nuclear bomb.
The UN atomic watchdog, meanwhile, says "overall, credible" evidence exists that until 2003, and possibly since, Iran conducted nuclear weapons research despite its repeated denials.
Israel, the sole but undeclared nuclear state in the Middle East, and the United States have refused to rule out a military strike against Iran.
Tehran has warned against an attack on its nuclear facilities, but at the same time argues that its programme would not be stopped even if it was bombed.
Its defiance is also reflected in other key challenges to the Islamic regime, with Iranian officials regularly dismissing an economic and diplomatic embargo and asserting that such efforts fail to isolate the country.
Repeated declarations about how the Jewish state's days are numbered despite Western efforts to shore up Israel are also common in Tehran.