In an interview afterward, he said he was able to take samples from two people; the crush of patients was too overwhelming to do more. He worried about preserving them; with electricity working only sporadically, there was no constant refrigeration.

“with some degree of varying confidence,” Mr. Hagel said — that the Syrian government had used chemical weapons.

Mothers are desperate to have their children vaccinated; patients with chronic conditions like heart disease and diabetes struggle to get medicine; and there is “huge anxiety in the population,”

On Aug. 21, the group got word from some of its “silent partner” hospitals of a flood of patients with “neurotoxic symptoms” — roughly 3,600 in a period of three hours, including 355 who died.

The debate over whether doctors should expose human rights abuses has long been “one of these inside baseball arguments within the humanitarian community,” said Len Rubenstein, an expert on human rights and medical ethics at Johns Hopkins University. While Doctors Without Borders has a culture of “bearing witness,” he said, not all humanitarian organizations do.

The International Committee of the Red Cross, for instance, adheres to a strict code of political neutrality;