Gail Minglana Martinez, 41, was traveling with her husband, Lieutenant Colonel Kato Martinez, and their four children when she was injured in one of the suicide bombings on March 22, Texas Congressman Blake Farenthold said in a statement.
It was unclear whether she was at the Brussels airport or a central metro station that were both targeted in the attacks.
Kato Martinez and the four children were also injured in the blast. They remain hospitalized, Farenthold said without elaborating about their conditions.
The family was living in Brunssum, the Netherlands, where Martinez is assigned to the Joint Force Command, the newspaper reported.
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"Gail was special to so many people. She blessed people's lives and made this world a better place," Minglana Martinez's brother told the paper.
Officials have not yet identified the fourth American killed in last week's bombings.
The Islamic State group claimed responsibility for the attacks, which killed at least 35 people and left some 300 wounded.