The cheque has been sent. That is the message from the White House today after the father of a slain US Army sergeant said a generous offer from President Donald Trump had not materialised.

Key points: Trump offered family of slain US soldier $25,000 from his "personal account"

Trump offered family of slain US soldier $25,000 from his "personal account" Father says cheque never arrived but White House says it is now "sent"

Father says cheque never arrived but White House says it is now "sent" Trump's chief of staff 'disgusted' military deaths are being 'politicised'

Chris Baldridge told The Washington Post that Mr Trump offered his family $US25,000 after the death of his 22-year-old son at the hands of an Afghan police officer in June.

"He said, 'I'm going to write you a cheque out of my personal account for $25,000', and I was just floored," Mr Baldridge said.

"I could not believe he was saying that, and I wish I had it recorded because the man did say this.

"He said, 'No other president has ever done something like this', but he said, 'I'm going to do it'."

But Mr Bainbridge told the newspaper the money never arrived, only a condolence letter.

"I opened it up and read it, and I was hoping to see a cheque in there, to be honest," the father said.

"I know it was kind of far-fetched thinking. But I was like, 'Damn, no cheque'. Just a letter saying 'I'm sorry'."

Army Sergeant Dillon Baldridge was shot by an Afghan police officer. ( US Army )

A White House spokeswoman said the media was advancing a "biased agenda" by following up on the Baldridge story.

"The cheque has been sent," White House spokeswoman Lindsay Walters said in an email.

"It's disgusting that the media is taking something that should be recognised as a generous and sincere gesture, made privately by the President, and using it to advance the media's biased agenda."

According to The Washington Post, it took former president Barack Obama 18 months to fulfil a similar promise to the family of Kayla Mueller, who was killed while being held captive by Islamic State in Syria in 2015.

The undisclosed sum to a charity set up in the 26-year-old's name only arrived after a media report about its absence, the newspaper said, with Mr Obama describing it as an oversight.

Trump in hot water with Gold Star families

The issue added to an already existing controversy over Mr Trump's response to military families who have lost loved ones.

On Monday, Mr Trump said some of his predecessors "didn't do anything" to console relatives of fallen soldiers, drawing widespread criticism.

He offered no evidence to back up his claim and it was immediately shown to be false.

Despite Mr Trump's boast that he calls all or nearly all military families when they lose a loved one, relatives of at least a half dozen people who died in military service since he became President have said they never got a call from him about their loss.

It also drew a swift response from Mr Obama's foreign policy adviser Ben Rhodes, who said it was "an outrageous and disrespectful lie".

Mr Trump made the claims in response to questions about why he had not publicly spoken about four servicemen killed in the African nation of Niger earlier this month.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 16 seconds 1 m 16 s Body of Special Forces soldier killed in Niger arrives in US (Image Reuters: Courtesy Aaron J. Jenne/ US Air Force)

He backed up his comments by suggesting the family of his chief of staff John Kelly, whose son was killed while serving in Afghanistan, may not have received a call from Mr Obama.

The Trump administration has since said General Kelly is "disgusted" that dealing with military deaths has become "politicised".

White House spokeswoman Sarah Huckabee Sanders said General Kelly was frustrated that "the focus has become on the process and not that American lives were lost".

Asked if Mr Trump politicised General Kelly's son's death, Ms Huckabee Sanders said: "He was responding to a question and stating a fact."

Trump accused of 'disrespecting' slain soldier's family

Then, on Wednesday, Mr Trump denied an account by congresswoman Frederica Wilson of Florida, who said the President told a grieving widow that her husband knew "what he signed up for".

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

Ms Wilson said she was in a limousine with the widow of Sergeant La David Johnson, on the way to greet his coffin off the plane, when the phone call happened.

"I didn't say what that congresswoman said," Mr Trump told reporters.

"I had a very nice conversation with the woman, with the wife who … sounded like a lovely woman," he said.

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But Sergeant Johnson's mother, Cowanda Jones-Johnson, told The Washington Post she was present during Mr Trump's call and supported the congresswoman's account of Mr Trump's comment.

"President Trump did disrespect my son and my daughter and also me and my husband," Ms Jones-Johnson said.

Asked by reporters about an earlier tweet saying he had "proof" of what he said, Mr Trump said: "Let her [Wilson] make her statement again and you'll find out."

The White House condemned Ms Wilson's claims as "appalling and disgusting".

Sergeant Johnson was one of the soldiers killed in Niger.

Sorry, this video has expired White House calls congresswoman's remarks about call to soldier's widow 'disgraceful'

Reuters/AP