Moments before the deadly bombings, siblings Alexander and Sascha Pinczowski called their family Tuesday morning to check in.

The two had made it to the airport in Brussels and were about to fly back to New York City, where they live.

Then came a roaring explosion and the sound of shattering glass.

Then, silence.

The phone line died — and they haven’t been heard from since.

The account of the phone call comes from the Dutch newspaper Algemeen Dagblad, which reported on their mother’s plight to find them.

The Islamic State has claimed responsibility for the bombings at Brussels Airport and a metro station that killed at least 31 people and injured many more. Others are still missing, their fates not yet known.

State Department spokesman Mark Toner said Wednesday morning that about a dozen U.S. citizens were injured in the attacks, though the department is not aware of any U.S. citizens who have died.

“We must emphasize that a number of U.S. citizens remain unaccounted for,” he said.

In the hours since the attacks, family, friends and lovers have pleaded for information about the Pinczowskis’ whereabouts, and photos of the two have been shared widely across social media.

The siblings had been visiting the Netherlands, according to CBS New York. Their father is from Maastricht, a town in the Netherlands, according to Algemeen Dagblad.

Since their disappearance, their mother has been scouring social media, trying to find people who know them or might have seen them, according to the Dutch newspaper.

Family members were traveling to Brussels to continue the search, according to reports.

Karen Van Suijdam, who said she is a friend, posted on Facebook, saying: “We are still looking for our friends Alexander Pinczowski and his sister Sascha Pinczowski.”

We are still looking for Alexander Pinczowski and his sister Sascha. They are missing in the Brussels airport attack…

Posted by Karen Van Suijdam on Tuesday, March 22, 2016

One person replied: “Dear Karen, Alex is a close friend from university. I have shared your statuses with my Brussels-based friends. Please keep us updated.”

Another commented: “Karen — please update me on their status as soon as you know. Sasha was in my class in school and this is very distressing!”

Mafalda De Andrade Vasconcelos urged others to help the family find them.

“Their mother is worried sick since she can’t get hold of them since this morning when they were checking in at Zaventem airport,” the Facebook user said. “If you have friends that work in hospitals or emergency centres, please share with them so that if they recognise them they may get the police to contact the parents.”

A woman who said she is Alexander Pinczowski’s girlfriend asked people on Twitter for help.

Sascha Pinczowski’s friend, Alex Kneeshaw, told the New York Daily News that the “news breaks my heart beyond belief.”

“I have known the Pinczowskis for over 15 years,” she told the tabloid. “We lived in Germany together where I met the whole family and have been a part of it ever since. She is the kindest, goofiest, and down-to-Earth girl I have ever met.

“She is the only friend that after a year or two of not seeing her we could sit down and act like no time had passed.”