UNITED NATIONS — President Obama made his case to the United Nations on Wednesday for a more forceful, coordinated global response against Islamic militants in the Middle East that would seek to dismantle their “network of death.”

In a speech to the U.N. General Assembly in New York, Obama used graphic language to condemn the methods of the “Islamic State” group that has taken over swaths of Iraq and Syria, saying it had used rape as a weapon of war, gunned down children, dumped bodies in mass graves and beheaded their victims.

Obama, who this week expanded the U.S.-led military campaign into Syria with support from five Arab nations, warned “Islamic State” fighters to “leave the battlefield while they can.” Before the president spoke, U.S.-led airstrikes for the third time this week pounded targets.

“Today, I ask the world to join in this effort,” Obama said. He said more than 40 nations have offered to join the coalition against the militants in Iraq and Syria.

British Prime Minister David Cameron, who spoke at the United Nations later in the day, was among world leaders weighing whether his country would join the military drive.

The president’s over-arching message was aimed at bolstering the fight, both militarily and diplomatically.

Obama used his annual speech to the 193-nation General Assembly to address a host of problems facing the world, from Russia’s interference in Ukraine, to the deadly Ebola virus in West Africa and the Israeli-Palestinian conflict, while also recognizing that the United States had its “own racial and ethnic tensions.”

In a departure from his prepared text, Obama urged Israel to extend an olive branch to the Palestinians after a summer of violence in Gaza.

Too many Israelis, he said, were ready to abandon the hard work of peace and added that this was something “worthy of reflection within Israel.”

“Because let’s be clear: the status quo in the West Bank and Gaza is not sustainable. We cannot afford to turn away from this effort,” he said.

The “worthy of reflection” comment was unlikely to be warmly received by Israeli Prime Minister Benjamin Netanyahu, who has a rocky relationship with Obama and will meet him at the White House on Oct. 1.

Cameron set out his position on “Islamic State” in his U.N. speech. He said parliament would be called back into session on Friday to approve air strikes.  

Many of Islamic State’s estimated 30,000 members are foreigners who flocked to the fighting.

The U.N. Security Council approved a resolution on Wednesday urging governments to clamp down on the travel and financing of the group.

In his speech, Obama, who has been stymied in trying to resolve long-festering disputes in the Middle East, called for a broader negotiation in which major powers address their differences directly “rather than through gun-wielding proxies.”

On Iran, Obama said, “My message to Iran’s leaders and people has been simple and consistent: do not let this opportunity pass. We can reach a solution that meets your energy needs while assuring the world that your program is peaceful.”