Iran faces its toughest sanctions for failing to comply with UN demands over its nuclear enrichment, the US says.

美国称，伊朗因未能按照联合国提出的核浓缩要求将面临其史上最严厉的制裁。

solely¹ at peaceful energy use" width="226" height="170" src="/upimg/100609/4_060038_1.jpg" />
Iran says its nuclear programme is aimed solely at peaceful energy use

The Security Council is set to vote on a fourth round of sanctions to tighten² financial curbs³ on Iran, while expanding a limited arms embargo⁴（武器禁运） .

US Secretary of State Hillary Clinton said they were "the most significant sanctions that Iran has ever faced".

But Iran's president warned his country would not agree to nuclear talks if the sanctions were imposed（强加） .

Mahmoud Ahmadinejad also said that a nuclear fuel-swap deal brokered⁵（以中间人身份安排） by Turkey and Brazil was an offer that would not be repeated.

Iran agreed in May to deposit 1,200kg of low-enriched uranium with Turkey, in return for reactor⁶ fuel, but the US and its Western allies said the agreement was too little too late.

They fear Tehran is secretly trying to build a nuclear bomb. Iran says its programme is aimed solely at peaceful energy use.

Kill negotiations⁷?

There have been three rounds of UN sanctions against Iran, blocking trade of "sensitive nuclear material", freezing the financial assets of those involved in Iran's nuclear activities, banning all of Iran's arms exports and encouraging scrutiny⁸（监视，审查） of the dealings of Iranian banks.

The new set of proposed sanctions is aimed at putting pressure on Tehran to stop enriching uranium.

Although it was watered down during negotiations with Russia and China on Tuesday, it does tighten existing restrictions⁹ on areas like shipping¹⁰ and finance.

Its proposals include:
Prohibiting（禁止） Iran from buying several categories of heavy weapons including attack helicopters and missiles
Urging all states to inspect cargo¹¹ suspected of containing banned items to and from Iran in their territory, including seaports¹² and airports
Calling on countries to block financial transactions and ban the licensing¹³ of Iranian banks if they suspect a link to nuclear activities
Increasing the number of individuals - reportedly including senior nuclear officials - and companies targeted with asset（资产，优点） freezes and travel bans

Mrs Clinton was upbeat about the prospect¹⁴ of of the new resolution, which has the support of all five of the UN's veto-holding members.

"The amount of unity¹⁵ that has been engendered¹⁶ by the international community is very significant," she said during a press conference with Ecuadorian President Rafael Correa in Quito.

Brazil and Turkey - also security council members - say the sanctions will kill attempts to revive（苏醒，复苏） negotiations with Iran, and put that case forward in a last-minute special session at the UN on Tuesday.

Despite their reservations, though, the BBC's Barbara Plett at the UN headquarters in New York said there was little doubt the resolution will be adopted.

While Turkey, Brazil and Lebanon are not expected to back the resolution, none of them has a veto.

Western diplomats¹⁷ expect 12 countries on the 15-member council to vote for the measure.