U.S. Defence Secretary Robert Gates says it will take Iran one to three years to develop a nuclear device. (Carolyn Kaster/Associated Press)

It will take Iran at least a year and perhaps three to produce a nuclear device, U.S. Defence Secretary Robert Gates said Friday.

It will then take more time for Iran to produce a weapon and a system for getting it to a target, Gates said at the meeting of NATO defence ministers in Brussels.

"But clearly, them getting to the threshold of having weapons is what concerns everybody, and not the other things, and in that area I would say there is a range there from [one to three] years," Gates said.

The time range is based on different intelligence estimates.

Iran insists its nuclear program is purely peaceful, aimed at producing nuclear energy and medical isotopes, but the United States and many allies believe Tehran's real goal is to build weapons.

Gates also said he was disappointed that Turkey voted Wednesday against a UN Security Council resolution to toughen sanctions against Iran.

Turkey and Brazil, which also voted against the resolution, had brokered a fuel-swap agreement with Iran that they hoped would address concerns Tehran was enriching uranium for nuclear weapons.

They hoped the deal would avoid the Security Council action, but the 12 countries that voted for the sanctions were not sure the swap would work. Lebanon abstained.

The sanctions would ban Iran from buying certain weapons, including attack helicopters and missiles, which could be used to deliver a nuclear attack.

The sanctions would also target financial institutions and individuals suspected of having ties to Iran's nuclear program.

On Friday, Iranian President Mahmoud Ahmadinejad said the sanctions were nothing but "a piece of paper. A worthless paper."

With files from The Associated Press