"The place that was hit was filled with civilians. It was a residential area, not a military warehouse," Abdullah al-Hussein, a Syria Civil Defense volunteer at the scene, told ABC News in a voice recording in Arabic on Wednesday.
“Yesterday evening we found a whole family in a shelter killed from choking on chlorine gas and today we found another family in a shelter that had also choked to death. We are finding whole families killed,” al-Hussein said.
Today, warplanes targeted the town of Khan Sheikhoun again, according to the Syrian Observatory for Human Rights and the White Helmets.
Abdulhai Tennari, a lung doctor in Idlib, told ABC News in a Skype interview that he treated 22 patients, including around eight children, after Tuesday's attack. His hospital is located about 40 miles away from Khan Sheikhoun.
“Many parents were looking for their children,” he said. “They don't know what happened with them because patients were distributed to many hospitals. Many people died, parents died, so because of this there were many children without families and nobody knew who they were.”
One of the children was only a few months old, he said.
"They were small children," he said. "One of them was breastfeeding, maybe a few months old ... he was trying to suck his finger. He wanted milk. We brought to him a bottle of milk but he didn’t take it. We looked for his parents and we found someone who knows them and transported him to them."
Tennari and other medics told ABC News that more than 500 people were injured in the attack that they said involved Sarin gas. Many patients died immediately, Tennari said.
“They had difficulty breathing and secretions in their lungs and very constricted pupils,” he explained. “The patients improved after we gave them the antidote. For this reason, we believe that it was Sarin.”
“MSF medical teams also visited other hospitals treating victims of the attack, and reported that they smelled of bleach, indicative of possible exposure to chlorine. These reports strongly suggest that victims of the attack on Khan Sheikhoun were exposed to at least two different chemical agents,” MSF said in a statement.
“How many more children need to die before Russia cares?” she said. "When the U.N. consistently fails in its duty to act collectively, there are times when we are compelled to take our own actions.”
The president called the suspected chemical attack "horrible" and "unspeakable," adding a "you'll see" when asked if he will take any action against Syria.
ABC News' Pete Madden and Katherine Faulders contributed to this report.