Mr. Carter and three former leaders from Europe arrived in Beijing on Sunday. Traveling with Mr. Carter were the former president of Finland, Martti Ahtisaari; Gro Harlem Brundtland, a past prime minister of Norway; and the former president of Ireland, Mary Robinson. The four are members of The Elders, an independent group of world leaders founded by Nelson Mandela.

“Clearly there is a great level of mistrust between North and South Korea,” Mr. Ahtisaari said. “But the stakes are too high to allow this standoff to continue.”