UNITED NATIONS -- President Barack Obama said Wednesday that the world stands at a crossroads "between war and peace," where it must choose international cooperation to build on the successes of the past or risk devolving into an unstable future.

Obama, in his annual address at the UN General Assembly, vowed the United States would lead in vanquishing the terrorist organization Islamic State.

"Fellow delegates, we come together as United Nations with a choice to make," he said. "We can renew the international system that has enabled so much progress, or we can allow ourselves to be pulled back by an undertow of instability. We can reaffirm our collective responsibility to confront global problems, or be swamped by more and more outbreaks of instability."

Obama, who was the second speaker following Brazil's President Dilma Rousseff in the General Debate portion of the General Assembly, touched on the perils in the world -- including U.S. racial tension in the form of civil strife in Ferguson, Missouri, the Ebola virus ravaging West Africa, barbaric violence by terrorist cells and state-sponsored aggression.

All these problems are best dealt with through collective action under the international system, Obama said.

During the speech, the president focused on unrest in the Middle East, outlining a wish list of four major actions for the world community -- destroy the Islamic State, reject extreme ideology, curb sectarian violence and encourage youth to reach their potential.

He singled out the threat from Islamic State, also known as ISIS and ISIL, as a grave concern that the United States is ready to address. Indeed, U.S. fighter planes began concerted attacks in Syria two days before the start of the gathering and have been firing on the group in Iraq for several weeks.

At a Security Council meeting later Wednesday that Obama presided over, the 15-member body voted unanimously on a resolution that requires nations to discourage and prevent their citizens from joining up with terrorist groups. The resolution was drafted under Chapter VII of the UN Charter, which allows sanctions and military action to enforce it.

But Obama implored Muslims to help out by rejecting the extremist ideology that gave rise to such ultraviolent groups as al-Qaida, Islamic State, Al Nusra Front, Boko Haram and others and urged them to cut off financial support that has allowed the militant groups to survive.

"Ultimately, the task of rejecting sectarianism and extremism is a generational task -- a task for the people of the Middle East themselves," he said in a 40-minute speech. "No external power can bring about a transformation of hearts and minds."

Obama reassured the group of heads of state and government in the General Assembly Hall that he has not forgotten the decades-old conflict between Palestinians and Israelis, who are fresh from a short but intense war in Gaza that claimed the lives of more than 2,000 Palestinians and several dozen Israelis.

The flare-up was perhaps the most jarring reminder that Obama's pledge to broker a peace agreement where the two entities would live as two independent states, which seemed promising a year ago, is now far from realization.

Obama had harsh words for Russia, calling its adventures in Ukraine "aggression" reminiscent of a previous era of international expansionism.

He accused Russia of arming pro-Kremlin separatists, refusing to allow access to the site of the downed Malaysia Airlines plane and sending troops into Ukraine.

"This is a vision of the world in which might makes right, a world in which one nation's borders can be redrawn by another, and civilized people are not allowed to recover the remains of their loved ones because of the truth that might be revealed," he said. "America stands for something different."

Iran, Obama said, continues to plague international affairs as the prospect of its nuclear program being used for military purposes is the subject of six-party talks that have stalled amid disagreements.

"My message to Iran's leaders and people is simple: Do not let this opportunity pass," Obama said.

"We can reach a solution that meets your energy needs while assuring the world that your program is peaceful."

Phyllis Bennis, director of the new internationalism project at Institute for Policy Studies in Washington, said the speech struck her as bellicose.

"The speech was carefully crafted to avoid sounding like a war speech but in actual terms of what the U.S. was supposed to do, it was precisely a war speech," she said.

Katie Laatikainen, director of the international studies program at Adelphi University in Garden City, called Obama's speech "refreshing" in that he named nations.

"I thought that it was sort of a combative speech by President Obama," she said. "There was a lot of pointing of fingers, which is in some ways refreshing. He called out Russia on Ukraine, and called on China to act as a great power and take on greater responsibility. In some ways that combativeness is also a way to build support for a broader coalition against ISIS."