CAMEROON, Cameroon -- More world leaders step up to the podium at the UN General Assembly on Wednesday but the lion's share of attention will be down the hall where U.S. President Donald Trump will be chairing the Security Council.

It'll be Trump's first experience in leading a session of the UN's most powerful body, where the U.S. currently holds the rotating presidency -- a perch it is using to double down on its criticism of Iran.

While Wednesday's meeting of the council will be addressing the issue of nonproliferation of nuclear, chemical and biological weapons, Trump himself has left little doubt that it'll be another chance to target Tehran.

On Tuesday, during an unabashedly "America First" speech, Trump said Iranian leaders "sow chaos, death and destruction" and "spread mayhem across the Middle East and far beyond." His national security adviser, John Bolton, warned that there would be "hell to pay" if Tehran crossed the U.S., its allies or their partners.

Iranian President Hassan Rouhani responded by accusing the Trump administration of violating the rules of international law and "state obligations" by withdrawing from the 2015 nuclear deal that Iran signed with the U.S. and five other major powers.

Rouhani is almost certain not to attend the Security Council meeting that will test Trump's ability to maintain diplomatic decorum and interact with representatives of rival nations.

The council is populated by five permanent members -- the U.S., China, Russia, Britain and France -- and 10 other member states, who occupy a council seat for two-year terms. Iran is not among them.

Business resumed Wednesday at the General Assembly, where 193 UN members were taking turns to speak out on pressing world issues and their national priorities in world affairs.

Panama's President Juan Carlos Varela Rodriguez kicked off proceedings. Among those scheduled to follow him were the leaders of Lebanon, Yemen, Colombia, Cuba, South Korea, Britain, Afghanistan and Italy.

This year, 133 world leaders have signed up to attend this year's assembly session, which ends Oct. 1, a significant increase from the 114 leaders last year.

However, America's go-it-alone attitude and growing divisions among key world powers risk eroding the UN's ability to bring positive change in global affairs and end conflicts in Syria, Yemen, and elsewhere.