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Iranian President Mahmoud Ahmadinejad appears at a news conference in Istanbul on Tuesday. ((Burhan Ozbilici/Associated Press))

The UN Security Council has approved a new round of sanctions against Iran over its refusal to curtail its nuclear program.

The resolution imposes a fourth round of sanctions against Iran and was approved Wednesday in New York. The final tally was 12 "yes" votes, two "no" votes from Brazil and Turkey and one abstention from Lebanon.

Turkey and Brazil brokered a fuel-swap agreement with Iran that they hoped would address concerns Tehran may be enriching uranium for nuclear weapons and avoid new sanctions.

"The goal of this resolution is to increase the cost to Iran's leadership for their continued defiance of the international community," said Susan Rice, the U.S. ambassador to the UN.

Rice said the financial and economic sanctions are also meant to persuade Iran that it's in the country's interest to peacefully resolve concerns about its nuclear program.

Speaking later Wednesday at the White House, U.S. President Barack Obama said the vote sends an unmistakeable message to Iran that non-peaceful nuclear activities will not be tolerated. If Iran does not respect its international obligations, Obama said, the nation will "find itself more isolated and less prosperous and less secure."

The sanctions would ban Iran from buying several categories of heavy weapons, including attack helicopters and missiles. The sanctions would also target financial institutions and individuals with suspected ties to the nuclear program.

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 atomic weapons.

Whether sanctions work is still an ongoing issue, Ken Taylor, who was Canada's ambassador to Iran during the 1980 hostage crisis, told CBC News Wednesday.

"But here it's not only the sanctions that are important. China and Russia signed on. That's a real milestone," Taylor said.

While "the sanctions themselves are not yet onerous ... given the passage with the concurrence of those two countries, [it] is really quite a significant step forward," Taylor said.

However, he noted, given Iran's record, the country is expected to largely ignore the sanctions, so there will likely be another series of even tougher sanctions.

The former ambassador called the Middle East situation Obama's primary foreign policy priority.

"This new stage of putting behind engagement and now going back to sanctions is going to be a test of really how well he's perceived in terms of bringing some resolution to the Middle East."

Toughest sanctions ever: Clinton

Speaking Tuesday from Ecuador's capital of Quito, U.S. Secretary of State Hillary Rodham Clinton called the proposed new sanctions against Iran's suspect nuclear program the toughest ever.

"I think it is fair [to say] that these are the most significant sanctions that Iran has ever faced," Clinton said at a news conference with Ecuador's president. "The amount of unity that has been engendered by the international community is very significant."

U.S. Defence Secretary Robert Gates said new sanctions would provide a "legal platform for individual nations to then take additional actions that go well beyond the resolution itself."

Iran recently agreed to ship much of its enriched uranium to Turkey in a nuclear fuel swap deal reached with the help of mediation from Brazil and Turkey.

Iran's UN ambassador, Mohammad Khazaee, said in an interview Tuesday with the Islamic Republic News Agency that the fuel swap would have led to "more constructive" regional and international co-operation, but moving ahead with sanctions shows some council members "prefer confrontation."

With files from The Associated Press