Two other aid workers for the group were kidnapped after Somali militants entered the Dadaab refugee camp in Kenya in October 2011. The two women were held hostage for 21 months before they were freed last month. Dr. Karunakara declined to comment on either the abduction or the release.

Founded in Paris in 1971 as Médecins Sans Frontières and often referred to by the French initials M.S.F., the group prides itself on being “neutral, independent and impartial.” Staff members deliver medical treatment to people affected by wars and natural disasters, to communities ravaged by epidemics and those that otherwise simply would not have access to medical services.

Its workers have a reputation as among the bravest in the field, often the first ones in when disaster strikes and the last to leave. In 1999, Doctors Without Borders was awarded the Nobel Peace Prize.

The group operates in some of the most dangerous places in the world, including Syria and Afghanistan. But the inherent and seemingly growing dangers of its work have become clear through a series of recent episodes.

In South Sudan this month, a group of armed men attacked a vehicle belonging to the group on the outskirts of the capital, Juba. Two staff members were wounded, one of them, identified only as Joseph, 28, died two days later. Doctors Without Borders requested an investigation into what the group’s director of operations, Marcel Langenbach, called a “brutal attack.”

Last week, the group announced that it would suspend activities in and around the town of Pinga in the Democratic Republic of Congo after its staff members there were threatened.

Dr. Karunakara said he had gone early in the morning to the Somali Embassy in Nairobi, Kenya, to break the news. He seemed visibly disappointed to have to make the withdrawal, calling it “undoubtedly the most difficult announcement I have had to make.”