The pregnant widow of a fallen United States soldier has contradicted President Donald Trump's account of his phone call about her husband's death, saying what he told her "made me cry even worse".

Key points: Ms Johnson says she was angry at his tone and that he forgot her husband's name

Ms Johnson says she was angry at his tone and that he forgot her husband's name Mr Trump responds on Twitter that he did not forget the name and said it without hesitation

Mr Trump responds on Twitter that he did not forget the name and said it without hesitation John McCain says "we should not be fighting about an American who lost his life"

Myeshia Johnson told the American ABC's Good Morning America program that a group of people listened to Mr Trump's call on speaker phone as they drove to receive Sergeant La David Johnson's body.

"The President said that he [Sergeant Johnson] knew what he signed up for, but it hurts anyway," Ms Johnson said.

"And it made me cry because I was very angry at the tone of his voice and how he said it. He couldn't remember my husband's name.

"The only way he could remember my husband's name was he told me he had my husband's report in front of him and that's when he actually said La David."

Bryan Black, Jeremiah Johnson, David Johnson and Dustin Wright were killed in an ambush. ( Supplied: US Department of Defense )

The comments back up those of Democratic Party politician Frederica Wilson — a close friend of the Johnson family who was a passenger in the car at the time, and who first publicised details of the phone call.

Mr Trump last week accused Ms Wilson of fabricating what he said during the call, tweeting that he had "proof" that this was the case.

In other tweets, Mr Trump called her "wacky" and accused her of "secretly" listening to the phone call.

Ms Johnson said everyone in the car was listening to Mr Trump's call.

"Whatever Ms Wilson said was not fabricated," Ms Johnson told Good Morning America, in her first interview since her husband's death.

"What she said was 100 per cent correct."

After the interview went to air, Mr Trump took to Twitter to dispute Ms Johnson's account of the conversation — specifically the claim that he had forgotten Sergeant Johnson's name.

Loading

'I don't have nothing to say to him'

Sergeant Johnson and three comrades died on October 4 in Niger when militants tied to the Islamic State attacked them.

Ms Johnson said she also wanted to know why she had not been allowed to see her husband's body. He was buried on Saturday.

"I need to see him so I will know that that is my husband," she said.

Sorry, this video has expired Body of ambushed soldier returns to US

"They won't show me a finger, a hand.

"I know my husband's body from head to toe. And they won't let me see anything.

"I don't know what's in that box. It could be empty for all I know.

"But I need to see my husband. I haven't seen him since he came home."

Ms Johnson said she wanted the world to know "how great of a soldier my husband was".

She also said he was "a loving and caring father and husband".

Asked if she had anything to say to Mr Trump now, Ms Johnson said: "No, I don't have nothing to say to him."

Sorry, this video has expired McCain's veiled criticism of Trump

Republican senator John McCain, a veteran who spent more than five years as a prisoner of war in North Vietnam and who chairs the Senate Armed Services Committee, said lawmakers want answers about the ambush in Niger.

"We should not be fighting about a brave American who lost his life serving his country. That should not be a topic in America today," he told the American ABC's The View program, adding that his committee needed more information about the incident.

In separate interviews, Republican senator Lindsey Graham and Democratic senator Chuck Schumer both said they backed Senator McCain's efforts to get more details, and that they had not been aware that the United States had so many military personnel in Niger.

US forces do not have a direct combat role in Niger, but they help its army with intelligence and reconnaissance in the government's efforts to target violent extremist groups.

AP