"The roadblocks may prove to be too great, but I firmly believe the diplomatic path must be tested," Obama said during an address to the U.N. General Assembly.
Obama issued a stern message to the international body itself, saying its ability to meet the test of the times is being challenged by the dispute over what to do about Syria's chemical weapons. He called on the U.N. Security Council to pass a resolution that would enforce consequences on Syrian President Bashar Assad if he fails to follow a U.S.-Russian deal to turn his chemical weapon stockpiles over to the international community.
Obama also announced that the United States would provide $339 million in additional humanitarian aid to refugees and countries affected by the Syrian civil war, bringing the total U.S. aid devoted to that crisis to nearly $1.4 billion.
As the General Assembly meetings opened, the situation in Syria was overshadowed by a flurry of friendly gestures between the U.S. and Iran's new government. Obama said recent statements by Iranian President Hasan Rouhani, a moderate cleric elected in June, should offer the basis for a meaningful agreement on Iran's disputed nuclear program.
The West has long suspected that Iran is seeking a nuclear weapon. Tehran has consistently denied the charge.
Obama, reflecting the skepticism of many in the U.S. and around the world, said Rouhani's "conciliatory words will have to be matched by actions that are transparent and verifiable."
Obama said he was asking Kerry to pursue diplomatic progress with Iran, in coordination with five other world powers. Kerry will join representatives from those nations Thursday in a meeting with Iranian Foreign Minister Mohammed Javad Zarif.
It's unclear whether Kerry and Zarif will meet one-on-one on the sidelines of that meeting. And Obama also offered no hints of whether he will meet Tuesday with Rouhani. Even a brief handshake would be significant, marking the first such encounter between U.S. and Iranian leaders in 36 years.
Obama arrived at the annual U.N. meetings with diplomatic opportunities, not only on Iran and Syria but also on the elusive effort to seal lasting peace between the Israelis and Palestinians. While the prospects of a peace accord remain as slim as ever, the two sides have resumed direct talks, partly as a result of months of lobbying by Kerry.
The president praised Israeli and Palestinian leaders for their willingness to take "significant political risks" in order to get back to the negotiating table.
"Now the rest of us must also be willing to take risks," he said, adding that the United States must recognize that Israel's security depends on the formation of a Palestinian state.
Obama will meet later Tuesday with Palestinian Authority President Mahmoud Abbas. He'll also hold talks at the White House next week with Israeli Prime Minister Benjamin Netanyahu.