US Claim of Sanctions Snapback Void of Legal Standing

The United States’ claim that all global sanctions on Iran have returned as of Sept. 20 was immediately rejected by both Iran and the European parties to the 2015 nuclear deal as lacking any legal effect, given that Washington is no longer a participant to the agreement, formally called the Joint Comprehensive Plan of Action. 
“The letter by the United States is null and void, has no legal standing and effect, and is thus completely unacceptable,” Iran’s Ambassador to the United Nations Majid Takht-Ravanchi said in a statement on Sunday, following a US announcement on Saturday evening about the resumption of UN sanctions on Tehran. 
In August, Washington initiated a 30-day process foreseen in JCPOA that could lead to the “snapback” of international sanctions on Tehran, after its bid to extend Iran’s arms embargo beyond its October expiration faced objection by the UN Security Council.  
The US had earlier quit the deal in 2018 and restored its unilateral sanctions on Tehran, but claimed that it was entitled to activate the snapback process since UN Security Council Resolution 2231 that endorsed the JCPOA still named it an “original participant”.
On Saturday evening, US Secretary of State Mike Pompeo announced that the deadline has passed and the UN resolutions against Iran have been automatically revived.
"The United States expects all UN member states to fully comply with their obligations to implement these measures,” he said in a statement, according to CNN. 

European Objection 

An overwhelming majority of the UN Security Council, including JCPOA members, expressed their opposition, calling the US move illegal in separate formal letters.
“US’ illegal & false ‘deadline’ has come and gone. UNSC member states continue to maintain US is NOT a JCPOA participant, so its claim of ‘snapback’ is null & void. US is STILL in violation of JCPOA and Res 2231—swimming against int'l currents will only bring it more isolation,” Takht-Ravanchi said on Twitter. 
The three European powers issued a joint statement on Sunday, recalling that the US notification circulated to the UNSC members is “incapable of having legal effect”, since it has ceased to be a JCPOA participant.
“Any decisions and actions which would be taken based on this procedure or on its possible outcome would also be incapable of having any legal effect,” France, Germany and the United Kingdom said in the statement, published on the British government’s website.
They also reaffirmed their commitment to uphold the authority and integrity of the UN Security Council and fully implement UNSCR 2231 that endorsed the JCPOA.
Josep Borrell, the European foreign policy chief, also stated the same argument in a separate statement. 
“Consequently, sanctions lifting commitments under JCPOA continue to apply,” he said Sunday. 
Borrell vowed to continue to do everything possible to ensure the preservation and full implementation of JCPOA by all and called on other members to refrain from any action that could be perceived as an escalation in the current situation.

Individual Enforcement

In view of all opposition, the US has threatened to use its own power to enforce the measures. 
“If UN member states fail to fulfill their obligations to implement these sanctions, the United States is prepared to use our domestic authorities to impose consequences for those failures and ensure that Iran does not reap the benefits of UN-prohibited activity," Pompeo said in his statement.
"In the coming days, the United States will announce a range of additional measures to strengthen implementation of UN sanctions and hold violators accountable," he added. 
Takht-Ravanchi called on the UN Security Council to block the US attempt to completely ruin JCPOA by creating “legal complications through presenting unilateral arbitrary interpretations and pseudo-legal arguments”.
“The Islamic Republic of Iran trusts that the members of the Security Council will, once again, reject the United States' continued attempt to abuse the Security Council's process, thus undermining the authority and credibility of the Council and the United Nations,” he said in his statement.