UNITED NATIONS — U.N. Security Council members were moved to tears Thursday as the first eyewitness to the latest suspected chlorine attacks on civilians in Syria emerged from the country to give a graphic eyewitness account of dying children.

A Syrian doctor who treated victims from a half-dozen attacks over the past month, Mohamed Tennari, was helped out of the country by the United States, which arranged for the closed-door briefing.

He showed a video of a suspected chlorine attack March 16 in his town of Sarmin in Idlib province, with images of three children, ages 1 through 3, dying despite attempts to resuscitate them. The medical area was so cramped that one of the children was lying on top of their grandmother, who also died.