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BRUSSELS — A New York-based brother and sister were among those killed during this week's Brussels attacks, a family spokesman confirmed Friday.

Sascha and Alexander Pinczowski had just arrived at the Brussels Airport when two explosions went off Tuesday. They had not been seen since, but on Friday they were confirmed as having died in the twin blasts.

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"We received confirmation this morning from Belgian authorities and the Dutch Embassy of the positive identification of the remains of Alexander and Sascha," James Cain, former U.S. ambassador to Denmark and a spokesman for the family, said in a statement. "We are grateful to have closure on this tragic situation, and are thankful for the loving support, thoughts and prayers from all."

Two of our own lost in the #brusselsattack. In memory of the Pinczowski siblings, we will continue to stand up to terror at every turn. — Bill de Blasio (@BilldeBlasio) March 25, 2016

The siblings, who were Dutch nationals, had been due to fly back to the U.S. at the time of the blasts.

Delta also confirmed Friday that some of its passengers were among those fatally injured in the departures area.

At least 31 people died and more than 270 were wounded in the explosions at the airport and another blast an hour later at a metro station. ISIS has claimed responsibility.

Earlier on Friday, a senior U.S. official told NBC News that two Americans had been confirmed killed in the attacks, without giving their identities.

Two other Americans, Justin Shults and his wife Stephanie, have not been heard from since the attacks, family members have said.

Alexander Pinczowski had been dating former Ambassador Cain's daughter, Cameron. The two planned on getting married, Cain said.