U.S. President Donald Trump goes before the United Nations Security Council on September 26 to make his case against Iran, one day after urging all nations at the UN to work with him to isolate Tehran's leaders.
But with key Iranian allies Russia and China sitting on the 15-member council, and Washington's European allies at odds with Trump over his decision to walk away from Iran's 2015 nuclear deal, the meeting may do little more than highlight the significant divisions over Iran among the world's powers.
Trump will be wielding the gavel because the United States this month holds the presidency of the Security Council, the top UN body dealing with pressing global security issues.
During his address to the General Assembly on September 25, Trump assailed Iran's leaders, accusing them of sowing "chaos, death, and destruction" throughout the Middle East and calling on world governments to join him in isolating Tehran.
Iranian President Hassan Rohani shot back in a speech hours later, denouncing what he called Washington's policy of disregarding international agreements and pursuing "might makes right" around the world. He also slammed the planned council meeting as a "preposterous and abnormal act."
The meeting will show a rift between the United States and its European allies over the Iran nuclear deal that Trump abandoned in May, claiming it would not prevent Iran from eventually developing nuclear weapons.
The United States has moved to reimpose sanctions that had been lifted under the landmark deal and has vowed to punish foreign firms that do business with Iran.
On September 24, the five remaining parties to the agreement -- Britain, China, France, Germany, and Russia -- announced that they would set up a special payment system to continue trade and business ties with Iran.
The United States initially said the council meeting chaired by Trump would focus on Iran but later broadened the agenda to include nuclear nonproliferation and weapons of mass destruction.
That opens the door to addressing allegations of chemical weapons use in Syria and Britain this year, as well as Trump's and the council's efforts to curb North Korea's efforts to develop nuclear weapons.
The usual practice is for the chair to speak last at council meetings, but in this instance Trump will be the first to address the chamber, followed by other heads of state.
French President Emmanuel Macron will address the council, as will British Prime Minister Theresa May. Russia and China will be represented by their foreign ministers, Sergei Lavrov and Wang Yi.
Iran has not requested to speak at the council meeting, diplomats said, although Rohani will hold a press conference soon after it is due to end.
It will be only the third time in UN history that a U.S. president will chair a Security Council meeting. Barack Obama presided over two meetings in 2009 and 2014.
U.S. Ambassador to the UN Nikki Haley said she expects Trump's appearance "to be the most watched Security Council meeting ever."
Trump is one of around 130 world leaders attending the UN General Assembly in New York, which formally began on September 25.