This time, however, the negotiations are being driven by a greater sense of international urgency.

The United Nations has issued dire warnings of potential famine in Yemen. In the United States, outrage over the killing of the Saudi dissident Jamal Khashoggi has increased broad pressure on the Trump administration to end military support.

It will be a delicate process. Initially, the rival delegations in Sweden will have no direct contact. Diplomats will shuttle between them in an effort to build common ground. Mr. Griffiths, the United Nations envoy, has said that the talks can succeed only if both sides “suspend their belief in the possibility of a military victory.”

Whether that is possible remains highly uncertain.

In the weeks before the talks, the United Arab Emirates, a key Saudi ally, pushed forward with a fierce offensive to snatch the Red Sea port of Hudaydah from Houthi control. Now coalition forces nearly surround the city, which is crucial to international aid efforts.

The United Nations hopes to broker a deal that would place Hudaydah under international control, effectively removing it from the strategic chessboard of the war and allowing relief to flow unimpeded into the country.