The United Nations Security Council is hours away from a scheduled vote on a new package of economic sanctions against Iran.
The vote, presumed to take place at 10am local time (1400 GMT) on Wednesday, is expected to target more than three dozen companies and individuals subject to a travel ban and an asset freeze.
Hillary Clinton, the US secretary of state, called the proposed sanctions, which resolution agreed to on Tuesday, the "most significant" ever against Iran.
"I think it is fair [to say] that these are the most significant sanctions that Iran has ever faced," she said. "The amount of unity that has been engendered by the international community is very significant."
The draft resolution - the fourth mandating sanctions against Iran - is sponsored by the five permanent members of the Security Council: the US, Britain, France, China and Russia.
In addition to the blacklist, it expands an existing arms embargo against Iran, and prevents the country from importing technology for certain kinds of ballistic missiles.
'Stick of resolution'
The Security Council announcement came several hours after Mahmoud Ahmadinejad, the Iranian president, warned that any new sanctions would end the prospect of negotiations over Iran's nuclear programme.
"The US government and its allies are so mistaken that if they think they can brandish the stick of resolution and then sit down to talk with us, such a thing will not happen," he said.
"We will talk to everyone if there is respect and fairness but if someone wants to talk to us rudely and in a domineering manner the response is known already."
Ahmadinejad also gave warning that a nuclear fuel swap deal reached last month - negotiated by Turkey and Brazil - could be scrapped if the UN approves new sanctions.
Under the proposed deal, Iran would ship 1200 kilograms of enriched uranium to Turkey in return for nuclear fuel for a reactor in Tehran.
The US and its allies have been indifferent to the proposal, saying it was not a serious offer.
The Iranian president had hoped that his warning, made at a regional security summit in Turkey, would sow seeds of doubt in the minds of Russian and Chinese leaders. Both are veto-wielding members of the council, and they have ensured that previous drafts of the resolution were watered down.
Alireza Ronaghi, Al Jazeera's correspondent in Tehran, said the sanctions under discussion at the UN would not have a drastic effect on the Iranian economy.
"It's important to remember that the Iranian economy has been under sanction for 30 years now," he said. "None of the sanctions are going to choke the Iranian economy."
'Window of opportunity'
Jorio Dauster, a former Brazilian ambassador to the European Union, told Al Jazeera that the new round of sanctions will be "counterproductive" for three main reasons.
"First of all, they [sanctions] will probably close the very narrow window of opportunity for negotiations that Brazil and Turkey called for a few weeks ago," he said.
"Secondly, I believe that those sanctions are going to increase the domestic support in Iran for Ahmadinejad and the Revolutionary Guard since they will be able to show that the major powers have once again treated Iran badly.
"And, finally, although the sanctions will impose an economic cost on Iran and some difficulties for the Revolutionary Guard, they will not in many ways impede the development of nuclear power."