SEOUL, South Korea — North Korean officials have a “tremendous sense of optimism” about their country’s recent turn toward diplomacy and have promised to work more openly with humanitarian aid groups, according to the head of the World Food Program, who visited the country last week.

David Beasley, the executive director of the United Nations agency, also said that while malnutrition continued to be a problem in the impoverished North, he saw no evidence during his four-day trip of the kind of extreme food shortages that killed more than two million people there in the 1990s.

“What I did not see was starvation,” Mr. Beasley said Tuesday at a news conference in Seoul. “I saw none of that. Is there undernutrition? Of course there is.”

Mr. Beasley said he spent two days visiting farms, villages, schools and nurseries in the poverty-stricken countryside and another two days in Pyongyang, the capital, talking with officials. The trip came a month before the North’s leader, Kim Jong-un, is scheduled to meet with President Trump in Singapore, on June 12.