Sen. Bernie Sanders (I-Vt.) on Sunday said the drone strike in Afghanistan that resulted in the deaths of 10  civilians was “unacceptable.”

“I certainly hope they understand what happened and make sure that never happens again. And this is not only a human tragedy, it reflects on us before the entire world. It’s unacceptable,” Sanders said of the Biden administration while appearing on CBS’s “Face the Nation.”

Sanders has previously been critical on the use of drone strikes, saying during his 2015 presidential campaign that he would move to limit them, though he did not say he would eliminate them outright.

On Friday, the Pentagon confirmed that it mistook a civilian vehicle for an ISIS-K threat on Aug. 29.

“I am now convinced that as many as 10 civilians, including up to seven children, were tragically killed in that strike,” said U.S. Central Command head Gen. Frank McKenzie.

“Moreover, we analyzed that it is unlikely that the vehicle and those who died were associated with ISIS-K or were a direct threat to U.S. forces,” McKenzie added. “Our investigation now concludes that the strike was a tragic mistake.”

A Pentagon official late last month called the drone strike an act of “self-defense” and said military officials were assessing the possibility of any civilian casualties.

It came after suicide bomber killed 13 U.S. service members and dozens of Afghans at a gate at the Kabul airport during evacuations. Officials blamed that attack on ISIS-K.

A family member of those killed in the drone strike said an apology from the U.S. was “not enough.”

“That is not enough for us to say sorry,” Emal Ahmadi, whose 3-year-old daughter was among those killed, told The Associated Press,

Ahmadi called for the person who fired the drone to be identified and punished. He also told the AP that he would be seeking financial compensation and relocation to a safer country.