Donald Trump’s chief of staff has told reporters he is “stunned” and “broken hearted” by the criticism of the US President’s call to the family of an Army sergeant killed in Niger.

Speaking in an unexpected and emotional appearance in the White House briefing room, Retired General John Kelly invoked the death of his own son, killed in Afghanistan in 2010, as he lashed out at Representative Frederica Wilson of Florida, who earlier this week said President Donald Trump had been disrespectful in his condolence call to the family of a soldier killed during an ambush in Niger.

Mr Kelly, speaking slowly and forcefully, said he was distraught that Ms Wilson overheard the conversation and was politicising what he called a “sacred” presidential effort to console the grieving loved ones of a slain soldier.

“It stuns me that a member of Congress listened in to that conversation,” Mr Kelly said.

“It stuns me. And I thought at least that was sacred.”

Mr Kelly told reporters that Mr Trump had expressed his condolences “in the best way that he could”.

“If you’re not in the family, if you have never worn the uniform, if you have never been in combat, you can’t imagine how to make that phone call,” Mr Kelly said.

Earlier this week, the aunt of Sergeant La David Johnson said President Trump had shown “disrespect” to the soldier’s loved ones as he telephoned them to extend condolences as they drove to a Miami airport to receive his body.

‘There’s nothing you can do to lighten the burden’

Florida Democrat Representative Frederica Wilson said Mr Trump had told the widow that her slain husband “knew what he signed up for”.

“Basically he said, ‘Well I guess he knew what he signed up for, but I guess it still hurts’,” Ms Wilson told CNN earlier this week.

Mr Trump has emphatically rejected Ms Wilson’s claims he was disrespectful, but he ignited a storm of his own this week when he boasted about his commitment to calling service members’ next of kin.

The US President also brought Mr Kelly into the controversy by wondering aloud if President Barack Obama had called the former Marine general after the death of Mr Kelly’s son in 2010.

The claim drew a swift response from Mr Obama’s foreign policy adviser Ben Rhodes, who said it was “an outrageous and disrespectful lie”.

Speaking at the White House, Mr Kelly confirmed on Thursday that Mr Obama had not called, but he made clear “that’s not a criticism”.

“That’s not a negative thing … I don’t believe all presidents call. I believe they all write,” he said.

Mr Kelly revealed that when Mr Trump took office, he urged the US President not to make those calls.

“I said to him, ‘Sir there’s nothing you can do to lighten the burden on these families’.”

A spokeswoman said Ms Wilson stood by her earlier comments, while the congresswoman herself, asked by local media in Florida about Mr Kelly’s remarks, replied only indirectly.

“Let me tell you what my mother told me when I was little,” Ms Wilson said.

“She said, ‘The dog can bark at the moon all night long, but it doesn’t become an issue until the moon barks back’.”

On Thursday, White House spokesperson Sarah Sanders addressed the controversy by telling reporters that Mr Kelly was frustrated that “the focus has become on the process and not that American lives were lost”.