There is little hope the 193-nation U.N. General Assembly will achieve much in the annual five-day marathon of speeches. But on the sidelines, U.S. officials plan to lobby allies for pledges of concrete military assistance to help defeat Islamic State, whose hardline Sunni Islamist fighters have taken over swaths of Syrian and Iraqi territory.
U.N. Secretary-General Ban Ki-moon said more than 140 heads of state or government will attend the assembly's annual "general debate", which begins on Wednesday and ends Sept. 30. He noted an unusually large number of serious conflicts: in the Middle East, Africa and Ukraine.
"The world is facing multiple crises," Ban told reporters.
"All have featured atrocious attacks on civilians, including children," he said. "All have dangerous sectarian, ethnic or tribal dimensions. And many have seen sharp divisions within the international community itself over the response."
U.N. officials and delegates say the top issue for Western and Arab leaders is the rampage of Islamic State militants, who are blamed for a wave of sectarian violence, beheadings and massacres of civilians.
"Together, we will address the horrendous violence in Syria and Iraq, where conflict and governance failures have provided a breeding ground for extremist groups," Ban said.
U.S. President Barack Obama is expected to use the U.N. podium on Wednesday to call for more countries to join his coalition of more than 40 nations to prevent IS from expanding its territory. The United States has been bombing IS targets in Iraq for the past month but has yet to bomb Syria.
The White House said it was unlikely that Obama would meet with Iranian President Hassan Rouhani while both are in New York this week. But Secretary of State John Kerry is expected to meet with Iranian Foreign Minister Mohammad Javad Zarif at which they are expected to discuss Iran's atomic program and IS.
On Friday, Kerry told a special meeting of the Security Council that Iran could play a role in helping tackle IS, an apparent shift in the U.S. position. Both Iran and the United States have ruled out military cooperation.
In addition to speeches by Obama, Rouhani and other high-profile leaders, other important attendees making their U.N. General Assembly debut this week include Egypt's President Abdel Fattah al-Sisi and Indian Prime Minister Narendra Modi.
On Wednesday, Obama will chair a rare summit meeting of the U.N. Security Council on the problem of foreign fighters. He last chaired a council summit in 2009 on eradicating nuclear weapons.
At Wednesday's meeting, the council plans to adopt a resolution demanding countries "prevent and suppress" recruitment and travel of foreign fighters to join extremist militant groups like IS by ensuring it is a serious criminal offence under domestic laws. Foreign fighters in IS are believed to be the group's cruelest.
U.N. member states will also tackle the Ebola crisis in West Africa. Obama and other leaders will also attend a high-level meeting on the exponentially worsening hemorrhagic fever outbreak that has devastated Liberia, Sierra Leone and other countries in the region.
The meeting comes just after the Security Council declared Ebola a "threat to international peace and security" and established the first-ever U.N. mission dedicated to tackling a public-health threat.
Since the current outbreak was first detected in March, Ebola has infected at least 5,357 people, according to the World Health Organization, mostly in Guinea, Sierra Leone and Liberia. It has also spread to Senegal and Nigeria. The virus has killed an estimated 2,630 people.
Liberian President Ellen Johnson Sirleaf had been due to speak at the General Assembly this week but canceled her trip to New York because of the Ebola crisis.
While the General Assembly speeches are going on, senior foreign ministry officials from the United States, Britain, France, Germany, Russia and China are meeting in New York with Iranian officials. They will try to break a deadlock in talks aimed at ending sanctions in exchange for curbs on Iran's nuclear program. Foreign ministers from the six powers may join the talks in the course of the week.
Even though a Nov. 24 deadline for a long-term deal is a mere two months away, diplomats close to the talks say a deal in New York is unlikely.
Just ahead of the General Assembly on Tuesday, U.N. chief Ban will convene a global summit meeting on climate change that aims to set the stage for a major environmental conference in Paris next year. Obama is expected to use the session to highlight strides the United States has made on climate change.
There will also be high-level side meetings on conflicts in Syria, Libya, South Sudan, Ukraine, the Central African Republic, Mali, the Israeli-Palestinian problem, and the U.N. war on poverty.