“We are united by our belief that diplomacy is the only way to resolve the nuclear crisis and threat of war now facing the Korean Peninsula,” said their letter to Mr. Trump, dated Wednesday. “Peace is the most powerful deterrent of all.”

A copy of the letter, signed by hundreds of female leaders, was made available in advance. It was also being sent to several senators who visited the White House for the briefing, said Christine Ahn, international coordinator for Women Cross DMZ, a group of female peace activists that helped organize the letter campaign.