Some reports from Tehran say people have been doing extra shopping on Friday, preparing for hard days if international sanctions return to haunt the troubled nation a few hours after midnight on Saturday.

The United States has promised to return all previous sanctions on Iran that were imposed by the United Nations Security Council before the 2015 Nuclear deal with Iran.

Many of those sanctions were lifted as Iran agreed to restrict its nuclear program and leave its uranium enrichment facilities open to international inspectors as part of the 2015 deal that was called the Joint Comprehensive Plan of Action.

The US notified the UN Security Council last month that it will activate the trigger mechanism of the JCPOA at midnight on Saturday September 20 as Iran has failed to stand by its obligations under the nuclear deal. But no one appears to know what awaits Tehran Sunday morning.

Washington announced the decision after UNSC members rejected a US proposal to extend the arms embargo on Iran which is scheduled to end by October 18. Both US allies and rivals, Russia and China have refused to back Washington's demands, but the US can simply announce that from its perspectives international sanctions are back.

The successful reimposition of American unilateral sanctions since 2018 proved that the US can force both governments and corporations to take note and be extremely careful not to violate those sanctions. So the questions is, why not try to unilaterally implement previous UN sanctions.

Although the details of how the scene would look like on Sunday, September 21 is not clear, Iran watchers are certain about one thing: The US will make sure that Tehran cannot purchase new weapons or sell its weapons to  others.

International relations expert Amir Ali Abolfath in Iran says "Previously, there were more UN sanctions than those imposed by the United States. But since President Trump took office, things have changed and the situation has turned the other way around. The US has sanctioned everything. Therefore, nothing new will happen after the activation of the trigger mechanism."

Abolfath says "The measure will only make the sanctions more costly [for the US] as it has to implement them unilaterally as during the past two months UNSC has refused to return the sanctions."

UN sanctions on Iran included restrictions passed between 2006 and 2015.  Resolution 2231 that was passed on July 20, 2015 was the last one of those ratifications. The first resolutions called on Iran to "suspend all enrichment-related and reprocessing activities." Later, they called for "suspending enrichment-related and reprocessing activities" and called on Iran to "cooperate with the IAEA, and imposed sanctions banning the supply of nuclear-related materials and technology, and froze the assets of key individuals and companies related to the program."

In 2010, Resolution 1929 "banned Iran from participating in any activities related to ballistic missiles, tightened the arms embargo, travel bans on individuals involved with the program, froze the funds and assets of the Iranian Revolutionary Guard and Islamic Republic of Iran Shipping Lines, and recommended that states inspect Iranian cargo, prohibit the servicing of Iranian vessels involved in prohibited activities, prevent the provision of financial services used for sensitive nuclear activities, closely watch Iranian individuals and entities when dealing with them, prohibit the opening of Iranian banks on their territory and prevent Iranian banks from entering into relationship with their banks if it might contribute to the nuclear program, and prevent financial institutions operating in their territory from opening offices and accounts in Iran."

Later resolutions extended sanctions that were imposed before 2010. After the nuclear agreement, Resolution 2231 made it clear that previous sanctions may return if Iran does not stand by its obligations.

Abolfath told Fararu news website in Tehran on Friday September 18 that "no new sanctions will be declared." However, he acknowledged that this is an unprecedented situation as far as the dynamics between the UN Chief and UNSC are concerned.

Meanwhile, Ali Bigdeli, another international relations expert in Tehran,  told reporters that President Hassan Rouhani's declaration of victory in the standoff with the US was premature "as no one knows what is going to happen." Rouhani congratulated the Iranian people for “the victory” coming on Saturday, insisting that the security Council will reject the US demand to restore international sanctions,

Bigdeli acknowledged that "The situation is highly sensitive as the United States has carried out covert diplomacy with Europeans and Russians during the past weeks." He added that unofficial reports from Geneva indicate that the IAEA is likely to announce that Iran has violated the JCPOA.

In another development, IRGC-linked news agency Fars quoted hardliner analyst Foad Izadi as suggesting that Iran should leave the Non-Proliferation Treaty (NPT) if the US takes a radical stance. He also suggested that Iran should continue to reduce its obligations under the nuclear agreement. However, he opined that Iran should not leave the JCPOA altogether.