Obama and Ban spoke with reporters after they met at the White House on a range of international issues, including Syria, North Korea and climate change.
"We started with Syria, where obviously the humanitarian crisis has gotten worse," Obama said, noting he and Ban agree "we are at a critical juncture."
The president said U.S. and U.N. officials will work together to try to find ways to reduce violence in Syria and foster a political solution to the civil war.
Obama told reporters there appeared to be "at least a window of opportunity for Israelis and Palestinians to go back to the negotiating table." Ban said he hoped the region would "fully utilize the momentum generated" by Obama's recent Middle East visit.
On North Korea, Obama said he and Ban agreed Pyongyang should "end the kind of belligerent approach that they've been taking. And to try to lower temperatures."
"Nobody wants to see a conflict on the Korean peninsula," the president said. "But it's important for North Korea, like every other country in the world, to observe the basic rules and norms that are set forth, including a wide variety of U.N. resolutions."
Group of Eight officials meeting in London issued a statement Thursday urging North Korea to tone down its "current aggressive rhetoric" toward the United States and South Korea, saying it could lead to further international isolation of Pyongyang.
British Foreign Secretary William Hague told reporters in London -- where talks are under way among the G8 nations of Britain, Canada, France, Germany, Italy, Japan, Russia and the United States -- the ministers expressed increasing concern about the growing jihadist presence in Syria. He said the trend offered a strong case for lifting the European Union's ban on arms shipments to the rebel movement.