Doctors Without Borders says a hospital it supports in Yemen was hit by a projectile Sunday morning, leaving at least four people dead and 10 injured.
The medical aid organization, also known as Médecins Sans Frontières or MSF, said more victims might still be trapped in the building's rubble.
On Oct. 27, a Doctors Without Borders hospital in Yemen was destroyed in an airstrike, the aid group says, and an MSF health center in the country was also hit on Dec. 3.
Sunday's strike "confirms a worrying pattern of attacks," Raquel Ayora, MSF director of operations, said in the statement.
MSF says it wasn't immediately able to confirm the origin of the attack.
A Saudi-led coalition, with U.S. support, has been carrying out airstrikes in Yemen for months, targeting Houthi rebels.
"All warring parties, including the Saudi-led coalition, are regularly informed of the GPS coordinates of the medical sites where MSF works," Ayora says. "There is no way that anyone with the capacity to carry out an airstrike or launch a rocket would not have known that the Shiara Hospital was a functioning health facility."
A U.S. airstrike in Kunduz, Afghanistan, in early October destroyed an MSF hospital, killing at least 30. The Pentagon called the attack "a tragic but avoidable accident."
MSF executive director Jason Cone called it "a serious violation of the law," in an interview with NPR in November.