A renowned female commander of the Kurdish opposition forces in Syria, credited by the U.S. military with saving American lives in the battle against ISIS, has been killed by a Turkish drone strike, according to two defense officials.

Salwa Yusuk, a deputy commander of the U.S.-backed Syrian Democratic Forces (SDF), was among three female SDF fighters killed in the strike last Friday, the officials said.

Yusuk, also known as Ciyan Afrin and Gian Tolhildan, had gained a reputation for her courage on the battlefield, her organization of women in the military and her astute military planning over the last 10 years.

“There is no doubt she saved American lives on the battlefield,” said a U.S. military official who requested anonymity because of the sensitivity of the situation.

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Yusuk and the two other SDF fighters — Joana Hisso, 30, also known as Roj Khabur, and Ruha Bashar, 19, also known as Barin Botan — were killed near Qamishli, Syria, when the car they were traveling in was targeted by a Turkish drone, the defense officials said. Yusuk was about 42 years old, according to a statement by the SDF.

(Left to right: Joana Hisso, Ruha Bashar, Salwa Yusuk)

In a tweet, U.S. Central Command called Yusuk “a critical SDF leader who led forces in combat vs ISIS since the height of the fight to defeat the vile ideology in NE Syria in 2017.”

Read more: NBC