At least four people were killed and 10 others were injured when a "projectile" hit a hospital supported by Medecins Sans Frontieres in northern Yemen on Sunday, the CNN cited the organization as saying in a statement.
Three of the injured were members of MSF, and two are in critical condition, the group said.
Several buildings collapsed and people may still be trapped in the rubble, according to MSF, also known as Doctors Without Borders.
"According to our staff on the ground, at 9.20am one projectile impacted the Shiara Hospital in Razeh district, where MSF has been working since November 2015," according to the statement.
"MSF cannot confirm the origin of the attack," the statement said.