More than 130 female activists from 38 countries pressed the leader of the United Nations on Tuesday to fulfill a goal he declared after assuming the job a decade ago: a permanent peace treaty to end the Korean War.

In an open letter to Secretary General Ban Ki-moon, a former foreign minister of South Korea whose tenure will expire at the end of the year, the women implored him to “lead the process of bringing formal closure to the longest standing war before you leave your post at the United Nations.”

The letter was co-sponsored by Women Cross DMZ, a group that organized a peaceful walk last year across the demilitarized zone separating North and South Korea, and the Women’s International League for Peace and Freedom, a prominent antiwar group that is more than 100 years old.

Mr. Ban, rumored to be contemplating a run to be president of South Korea after he leaves the United Nations, has often expressed a wish to reduce tensions on the Korean Peninsula.