Iran's foreign minister dismissed Saturday the threat of a US military strike against Tehran's nuclear sites, describing such warnings as an "old habit that dies hard" given ongoing diplomacy.

Mohammad Javad Zarif, who leads the Iranian side in talks with six world powers that aim to end the dispute over the Islamic republic's nuclear programme, said threats of conflict should be off the table.

He was responding to General Martin Dempsey, chairman of the US Joint Chiefs of Staff, who Thursday said "the military option... to ensure that Iran does not achieve a nuclear weapon is intact".

The United States has long said targeted bombing of Iran's nuclear sites and other key facilities may be needed if Tehran -- which denies seeking the bomb -- does not rein in its atomic activities.

But Zarif hit back at Dempsey, highlighting that his claim was old and discounting its validity given the talks aim to end the nuclear impasse and culminate in a final deal by the end of June.

"The military option is non-existent and doesn't work against Iran, and it's better to stop making those statements," Zarif said at a joint news conference with his Australian counterpart Julie Bishop.

"We don't pay attention to them because we know that there is none," Zarif said, again referring to the option of a military attack on Iran.

"The fact we are negotiating indicates that everybody understands the only way to deal with Iran is to recognise Iran's rights and have mutual respect.

"That will provide a far better answer than getting engaged in disastrous adventurism," he added.

Dempsey's comments came after Russian President Vladimir Putin lifted a ban on supplying S-300 missile systems to Iran. The US general said the move would not affect America's ability to conduct a military strike.

Russia's decision was condemned by Israel, the most vehement opponent of the talks between Iran and the five permanent members of the UN Security Council plus Germany.

Iran insists its nuclear programme is for peaceful energy development rather than military purposes.

Russia said progress in nuclear talks, which could see Iran agree to curbs and rigid inspections for at least a decade in exchange for sanctions relief, meant there was no longer a need for it to prohibit export of the S-300 surface-to-air missiles.

Iran, which hailed Russia's move as a step toward "lasting security" in the region, currently lacks advanced air defences that could knock out modern fighter aircraft in the US or Israeli air forces.

The S-300 is designed to detect and destroy ballistic missiles, cruise missiles and aircraft at low altitude.

Although the S-300 would provide a major improvement for Iran's air defences, it remains unclear if the missile would be a match for America's stealthy F-22 fighters and bombers, experts say.