WASHINGTON • White House Chief of Staff John Kelly has unequivocally defended US President Donald Trump's calls to the families of four fallen soldiers, using his credibility as a retired general who lost a son on the battlefield to help his boss contain a public relations crisis.

In an emotional appearance in the White House briefing room on Thursday, Mr Kelly described in painful detail the trauma of losing service members.

He also excoriated a Democratic congresswoman for publicising her account of Mr Trump's call on Tuesday with the widow of one of the four young men killed in an ambush in Niger.

The former homeland security secretary said that he thought Mr Trump spoke "bravely" and "expressed his condolences in the best way that he could".

"If you elect to call a family like this, it is about the most difficult thing you can imagine," Mr Kelly said. "There's no perfect way to make that phone call."

His voice growing thin, Mr Kelly expressed regret and apparent indignation that the commander-in-chief's interactions with Gold Star families had become a subject of public debate.

"I just thought that that might be sacred," Mr Kelly lamented.

Mr Kelly said he had advised Mr Trump not to make the calls because "it's not the phone call that parents, family members are looking forward to."

But, after taking advice, Mr Kelly said Mr Trump called four people.

"And in his way, tried to express that opinion that he's a brave man, a fallen hero, he knew what he was getting himself into because he enlisted... and was where he wanted to be, exactly where he wanted to be with exactly the people he wanted to be with when his life was taken. That was the message."

It was alleged that during a call, Mr Trump offended the pregnant widow of Sergeant La David Johnson, 25, who was killed in an ambush on Oct 4.

WASHINGTON POST, AGENCE FRANCE-PRESSE