BRUSSELS -- A brother and sister who had been living in New York were among those missing following the terrorist attacks in Brussels, Belgium, Dutch media reported.
Sascha and Alexander Pinczowski have family in the Netherlands but have been living in New York, CBS New York reports.
Many have been posting about their disappearance on social media.
They were reportedly on the phone with their mother when she heard an explosion and the phone call disconnected.
A couple with ties to Kentucky, Stephanie and Justin Shults, are also missing. The family has received conflicting reports about their status.
Betty Gragg-Newsom told CBS affiliate WKYT that her sister, Carolyn Moore, was in Brussels to visit them.
Moore was with Stephanie, her daughter, when the bombs went off at the Brussels airport at Zaventem.
"My husband called the American Embassy, and they're looking for her too," Moore told Belgian broadcaster RTL.
"We were hoping to hear something immediately that Stephanie and Justin had gotten to their car, or had gotten home, or had somehow gotten out of that airport," Newsom previously told WKYT.
Stephanie is a graduate of Bryan Station High School and Transylvania University, according to her aunt. She says Stephanie had received her master's degree at Vanderbilt and had recently moved to Brussels for work, WKYT reported.
Relatives say Stephanie Shults is from Lexington, Kentucky, and Justin Shults is from Gatlinburg, Tennessee. They were excited to live in Europe and traveled frequently.
Newsom says Stephanie works for Mars, Inc. in Brussels. The couple moved there in June of 2014.
The United States says some government personnel in Brussels are unaccounted for since the deadly airport and subway attacks.
State Department spokesman Mark Toner says the U.S. is still seeking to locate all its officials serving at the American missions to Belgium, the European Union and NATO, and their family members.
Toner says some still haven't been reached, without providing an exact number. He noted that Belgium hasn't released the identities or nationalities of those killed or in Tuesday's bombings, or injured and hospitalized.
The State Department said it does not know of any Americans killed in the Brussels attacks.
The Islamic State of Iraq and Syria, or ISIS, claimed responsibility for attacks in Brussels that killed at least 31 people and injured 270 others.
In the middle of a busy morning rush hour, two explosions hit the Brussels airport and a third struck in the city's Maelbeek metro station, which is near the U.S. Embassy and European Union headquarters.
So far, three men have been identified as possible suspects in the airport bombing. Authorities in Belgium said two men in a photo issued by police were "probably" suicide bombers while a third is being sought.
Federal police have issued a wanted notice for a man seen wearing a thick light-colored jacket with a black hat and glasses. They are urging the public to call them if they recognize the man.