“The resolution takes a maximalist position on Iran,” one diplomat told AFP.
Another said the draft “goes beyond the current provisions” of the ban on conventional weapons sales to Iran that ends on October 18.
The embargo is due to expire under the terms of a resolution that blessed the Iran nuclear deal, signed in July 2015 and officially known as the Joint Comprehensive Plan of Action (JCPOA).
Under the deal, negotiated by then US president Barack Obama, Iran committed to curtailing its nuclear activities for sanctions relief and other benefits.
President Donald Trump pulled America out of the accord in May 2018 and reinstated unilateral sanctions on Iran under his campaign of “maximum pressure.”
Iran has since taken small steps away from compliance with the nuclear accord in retaliation for the US withdrawal as it presses for sanctions relief.
US Secretary of State Mike Pompeo announced on Wednesday that the United States would put forward its resolution despite ardent opposition from Russia and China.
But UN diplomats have said opposition to the resolution’s current form is so widespread that Washington is unlikely even to secure the nine votes required to force Moscow and Beijing to wield their vetoes.
European allies of the United States – who along with Russia and China signed the deal with Iran – have voiced support for extending the conventional arms embargo but their priority is to preserve the JCPOA.
The US text effectively calls for an indefinite extension of the embargo on Iran and uses hawkish rhetoric.
Diplomats fear the resolution threatens the nuclear agreement. Iran says it has the right to self-defense and that a continuation of the ban would mean an end to the nuclear deal.
“The focus should remain on preserving the JCPOA,” a third diplomat said.
“It is the only way to provide assurances about the exclusively peaceful nature of Iran’s nuclear program. No credible alternative to this instrument has ever been proposed since the US withdrawal,” they added.
Experts say the gulf between the US and its allies threatens a summer of discontent at the Security Council as the October 18 deadline approaches.
“This is a car crash that everyone knows is going to happen,” New York-based UN expert Richard Gowan told AFP, describing the US draft as a “poison pill of a text.”
UN-watchers suggest that EU countries on the Security Council could be brought on-board by a short-term extension of the embargo if it helps preserve the nuclear deal.
Or members may propose their own draft resolution, but finding consensus is likely to be difficult with China and Russia intending to veto.
The United States has threatened to try to force a return of UN sanctions if it is not extended by using a technique called “snapback.”
Pompeo has offered the contested argument that the United States remains a “participant” in the nuclear accord as it was listed in the 2015 resolution – and therefore can force a return to sanctions if it sees Iran as being in violation of its terms.
European allies have been skeptical on whether Washington can force sanctions and warn that the attempt may delegitimize the Security Council.
Kelly Craft, the US ambassador to the UN, told journalists Thursday that Washington’s first objective was an extension but it is prepared to use “all tools available.”
A push for snapback “seems very likely,” according to Gowan, of the International Crisis Group think tank.
“At worst, that could torpedo the nuclear deal once and for all, which may be what Pompeo wants.”