Doctors Without Borders treated four patients showing symptoms of exposure to chemical agents, the charity said in a statement cited by The Newsweek.

The patients, an adult man and woman, a three-year-old girl and a five-day-old girl, were all from the same family.

The family lived in Marea, Syria, a town about 45 kilometers north of Aleppo. Their house had been hit by a mortar shell on the evening of August 21.

The family said that after the shell hit their house, yellow gas filled their home. The family was first treated at a local hospital before being moved to the Doctors Without Borders facility.

The family experienced difficulty breathing, skin inflammation, red eyes and conjuctivitis.

Several hours after seeking treatment, their conditions worsed as they developed blisters and their breathing became more difficult.

As a result, the family was moved to a specialized treatment facility.

"MSF has no laboratory evidence to confirm the cause of these symptoms. However, the patients’ clinical symptoms, the way these symptoms changed over time, and the patients' testimony about the circumstances of the poisoning all point to exposure to a chemical agent," Pablo Marco, the charity's program manager for Syria, said in a statement.

"Any use of chemical weapons constitutes an extremely severe violation of international humanitarian law," Marco said.