The administration of US President Donald Trump has said that all UN sanctions on Iran have become in effect, and that the conventional arms embargo imposed on Iran will not expire in mid-October.

But 13 countries out of 15 members of the UN Security Council - including longtime allies of the United States - said Washington's move was invalid.

Diplomats say only a few countries are likely to reimpose those measures that were lifted under the 2015 nuclear deal Iran signed with world powers aimed at preventing it from developing nuclear weapons.

US Secretary of State Mike Pompeo said in a statement, "The return to sanctions today is a step towards international peace and security. And in the coming days, the United States will announce a set of additional measures to strengthen the application of UN sanctions and hold violators accountable."

Here's a look at the events leading up to this confrontation, and what might happen next.

Why will the arms embargo on Iran end?

  • The UN Security Council imposed an arms embargo on Iran in 2007, and this ban is set to expire on October 18, under the 2015 nuclear deal between Iran, Russia, China, Germany, Britain, France and the United States.

  • The agreement prevents Tehran from developing nuclear weapons in exchange for sanctions relief, and the agreement was included in a Security Council resolution in 2015.

  • In 2018, US President Donald Trump withdrew from the nuclear deal concluded by his predecessor Barack Obama's administration, describing it as "the worst agreement ever."

  • The United States failed last month to try to extend the embargo on Iran at the Security Council.

What does this mean for the 2015 nuclear deal?

  • The parties that remained involved in the nuclear deal said they were committed to preserving it, and Iran said that the agreement would remain in effect despite the US move at the United Nations.

  • Britain, France and Germany told the UN Security Council on Friday that Iran's exemption from UN sanctions would continue beyond September 20.

  • The envoys of the three European parties wrote in a letter to the council, "We worked tirelessly to preserve the nuclear deal and we remain committed to that."

What penalties will return?

  • The return of UN sanctions would oblige Iran to suspend all enrichment-related and reprocessing activities, including research and development, and ban the import of anything that could contribute to those activities or the development of nuclear weapons delivery systems.

  • It will also include re-imposing an arms embargo on Iran, preventing it from developing ballistic missiles capable of launching nuclear weapons, and resuming specific sanctions against dozens of individuals and entities.

  • Countries will be urged to check shipments to and from Iran, and allow them to confiscate any prohibited shipment.

What led to that result?

  • The United States filed a complaint with the UN Security Council about Iran violating the nuclear deal last month.

  • Since the United States withdrew from the nuclear deal, Washington has imposed strong unilateral sanctions, in an effort to force Iran to return to negotiate a new agreement.

  • In response, Iran violated basic restrictions imposed by the agreement, including its stockpile of enriched uranium.

  • The United States says that according to a 2015 UN Security Council resolution that includes the nuclear deal in its system, it has activated a 30-day process to reimpose all UN sanctions on Iran.

  • Washington believes that despite its withdrawal from the nuclear agreement, the resolution still considers it a participating country.

  • The Security Council had to vote within 30 days on a resolution to continue to reduce sanctions imposed on Iran, and unless such a resolution is adopted by the deadline, all UN sanctions that were in effect before the 2015 nuclear deal will be re-imposed automatically, and no such resolution has been proposed. This decision to vote.

  • Last month, Indonesia - which was chairing the UN Security Council for the month of August - said it was "not in a position to take further measures" regarding the US attempt to activate the return of all international organization sanctions on Iran;

    Because the matter does not get unanimous within the Council.

  • 13 countries out of 15 on the Security Council say they oppose Washington's moves;

    It considers it invalid, given that it uses a process from within the nuclear agreement to which it is no longer a party.

  • Pompeo warned on Saturday that "if member states of the United Nations fail to fulfill their obligations to impose these sanctions, the United States is prepared to use its domestic powers to impose consequences for these failures."

What will the United States do now?

  • The US President intends to issue an executive order allowing him to impose sanctions on anyone who violates the United Nations conventional arms embargo imposed on Iran;

    In an attempt to strengthen America's insistence that the measure has been extended indefinitely beyond October 18 next.

  • The executive order is expected to be issued in the coming days, and it will allow the president to punish foreign violators, as US entities are already prohibited from carrying out any arms-related dealings with Iran, and denying them access to the US market.

How will an administration led by Democrat Joe Biden deal with Iran?

  • Three prominent Iranian officials said that the leadership in their country is determined to maintain its commitment to the nuclear deal, in the hope that Trump's Democratic rival, Joe Biden, wins the US presidential election on November 3, which may save the agreement.

  • Biden - who was Obama's deputy at the time of negotiating the nuclear deal - said that he would return his country as a party to it if Iran first came back to abide by all of its provisions.

  • "If Iran returns to strict adherence to the nuclear deal, the United States will return to join and build on the agreement, and will work with its allies to counter Iran's destabilizing actions," said Biden campaign spokesman Andrew Bates.