“He was supposed to be 21 on May 5. He was just a baby,” said Sgt. Declan J. Coady’s sister, Kiera

Declan Coady.

Army Sgt. Declan Coady.Credit : U.S. Army Reserve

The family of a 20-year-old American soldier killed this week in the war with Iran is remembering him as a “smart and kind and amazing” son and brother while sharing their heartbreak at not being able to speak with him even one last time.

Sgt. Declan J. Coady of West Des Moines, Iowa, was one of six Army reservists serving in Kuwait who were killed on Sunday, March 1, in an unmanned aircraft system — or drone — strike, according to the Pentagon.

The soldiers were in a command building at a port in Kuwait, according to ABC News.

They were part of Operation Epic Fury, the name given to the joint U.S.-Israel offensive against Iran that triggered the war as part of what the U.S. says is an effort to topple a hostile regime and curb Iran’s nuclear ambitions.

Now Coady’s family is speaking out.

“On Sunday, March 1, after trying to check in, we heard nothing. Trying to be positive we all assumed he was just in a situation where he couldn’t message back, but we all knew something was wrong,” his sister, Kiera, said in the statement, according to ABC News.

“At 8 p.m. as we all were getting ready to go to bed, the doorbell rang, and the rest of that night will forever be one of the worst nights of our lives. While it’s all blurry, we all knew what the doorbell meant,” she continued.

Coady, who enlisted in 2023, was Kiera’s younger brother and only two months away from turning 21.

He died en route to the hospital after the drone attack and was posthumously promoted from specialist.

“The only thing I can think is that I wish I had called him one more time and told him I loved him,” Kiera said in her statement. “I wish that I had been able to be there or trade places with him or anything just so he could have known he was safe and that we loved him and he didn’t need to be scared … He was just a baby.”

When Coady’s sister first received news of the drone strike, her instinct was to call him so he could tell her it wasn’t true, she said: “Maybe I would hear his voice telling us he was safe.”

“But there was nothing, not even a voicemail,” she said.

Never miss a story — sign up for PEOPLE’s free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer​​, from celebrity news to compelling human interest stories.

“I wish I could think of words beyond that he was smart and kind and amazing, but even if I were to throw in other words it still wouldn’t quite capture his spirit,” Kiera said. “He was truly a rock in all of our lives and was just the most amazing brother and son my family could have asked for.”

The others who died in the strike have been identified by the Pentagon as Sgt. 1st Class Nicole M. Amor, a 39-year-old Army Reserve soldier and mother of two; Capt. Cody A. Khork, 35; and Sgt. 1st Class Noah L. Tietjens, 42.

The names of the two other killed service members have yet to be confirmed.