A U.S. official told reporters in Brussels Friday that at least two Americans were among those killed in the terror attacks in that city Tuesday. It wasn't immediately clear who the official was referring to.
The word came with U.S. Secretary of State John Kerry visiting Brussels to express his condolences to the Belgian people.
In addition, family members said a brother and sister, both Dutch citizens who had been living in New York City and were among those missing following the Brussels attacks, were killed, their family says.
Sascha and Alexander Pinczowski have relatives in the Netherlands. They were returning to the U.S. when they lost their lives, CBS News was told.
A statement provided to CBS News early Friday on behalf of their family says, "We received confirmation this morning from Belgian Authorities and the Dutch Embassy of the positive identification of the remains of Alexander and Sascha. We are grateful to have closure on this tragic situation, and are thankful for the thoughts and prayers from all. The family is in the process of making arrangements."
Alexander Pinczowski was engaged to the daughter of James Cain, a former U.S. ambassador to Denmark.
Sascha and Alexander Pinczowski were reportedly on the phone with their mother when she heard an explosion and the phone call disconnected.
It wasn't immediately clear whether the siblings lost their lives in the blast at the Brussels airport or in the subway there.
Kerry, speaking after meeting with Belgian Prime Minister Charles Michel Friday, said the U.S. "is praying and grieving with you for the loved ones of those cruelly taken from us, including Americans, and for the many who were injured in these despicable attacks."
It wasn't clear which Americans Kerry was referring to.
A couple with ties to Kentucky, Stephanie and Justin Shults, remain among the missing. Their family has received conflicting reports about their status.
"The United States stands firmly with Belgium and with the nations of Europe in the face of this tragedy," Kerry said, adding that the world will not relent in its fight against the Islamic State group, which has claimed the attacks.
"We - all of us representing countless nationalities - have a message for those who inspired or carried out the attacks here or in Paris, or Ankara, or Tunis, or San Bernardino, or elsewhere: We will not be intimidated," he said. "We will not be deterred. We will come back with greater resolve - with greater strength - and we will not rest until we have eliminated your nihilistic beliefs and cowardice from the face of the Earth."
Michel thanked Kerry for his visit, calling it a powerful message of solidarity. "It is very important for us today to receive your support," he said. He offered condolences for the American victims and vowed to step up counter-terrorism cooperation with the U.S. and others.
Kerry said he offered the prayers of the American people for "these people who have suffered inconceivable losses."