US President Donald Trump told the widow of a soldier killed in an ambush in Niger that "he knew what he signed up for", a lawmaker has said.
Congresswoman Frederica Wilson said she heard some of the "insensitive" remarks made by phone while she was in a car with Sgt La David Johnson's family.
Mr Trump, she said, then added: "I guess it still hurt."
A White House official said Mr Trump's conversations with the families of fallen servicemen were private.
Sgt Johnson, 25, was among the four US soldiers killed in 4 October in an area where Islamist militants, including al-Qaeda fighters, operate. His widow, Myeshia, is expecting the couple's third child.
In an interview with CNN, Ms Wilson said Mr Trump's call happened shortly before Sgt Johnson's casket arrived in Miami: "Basically he said, 'Well, I guess he knew what he signed up for, but I guess it still hurt'."
The Democrat congresswoman said she listened to part of the conversation on speaker phone.
Talking to ABC News affiliate WPLG, Ms Wilson added: "Yeah, he said that. To me that's something that you can say in a conversation, but you shouldn't say that to a grieving widow.
"And everyone knows when you go to war, you could possibly not come back alive. But you don't remind a grieving widow of that. That's so insensitive."
The full context of the remarks are not known. Ms Wilson said that when she asked Ms Johnson about the exchange, she said she could not remember.
"She was just crying. She couldn't say anything. The only thing she said when it was time to hang up was thank you, bye-bye," she said on CNN.
The alleged remarks sparked angry comments on social media, with Ms Wilson saying on Twitter that Mr Trump did "not possess the character, empathy or grace to be president of the United States".
Mr Trump had been criticised for not contacting the families of the four soldiers killed right away. On Monday, he said he had written letters to the relatives and planned to call them soon.
The White House later said the president had spoken to the families, but did not say when.
On Tuesday, Mr Trump suggested that President Barack Obama did not call the family of his chief of staff Gen John Kelly when their son was killed in Afghanistan in 2010.
He made the comment in an interview to defend his claim that his predecessor neglected to call the loved ones of fallen soldiers. The remarks sparked outrage among Mr Obama's former aides.