Joe Biden was stunned into silence when he was told families of US service members killed in Kabul in August 2021 said that when the bodies were returned and the president met grieving relatives, he spent too much time talking about the death of his own son, Beau.

“I paused for the president to respond,” Jen Psaki, then White House press secretary, writes in a new book.

“The silence that followed was a bit too long. I worried for a moment that our connection had been lost.

“‘Sir, are you still there?’ I asked.”

Psaki left the White House in 2022, joining MSNBC. Her book, Say More: Lessons from Work, the White House and the World, will be published in the US next week. The Guardian obtained a copy.

On 29 August, the bodies of the Americans arrived at Dover air force base in Delaware, Biden’s home state. The president and the first lady, Jill Biden, attended.

“Of all the president’s duties,” Psaki writes, “this is high on the list of most heartbreaking. For President Biden in particular, it stirred feelings of his own despair about the death of his son Joseph Biden III, aka Beau.”

Beau Biden, a former attorney general of Delaware, went to Iraq with the national guard. He died of brain cancer in 2015, aged just 46.

Biden has questioned whether “burn pits” at US bases in Iraq might have caused his son’s cancer, championing legislation to help affected veterans. In her book, Psaki cites World Health Organization research which says burn pit emissions contain substances “known to be carcinogenic to humans”.

Psaki also notes how Biden endured the deaths in 1972 of his first wife, Neilia Biden, and their one-year-old daughter, Naomi, in a car crash in which Beau and his brother Hunter were critically injured. The president “often refers to these unique and disparate, but nevertheless unbearable, experiences of grief and loss as a way to connect with others”, Psaki writes.

But Biden’s visit with the grieving families at Dover stirred up significant controversy, and political attacks.

Psaki describes and dismisses as “misinformation” the claim, boosted by rightwing media, that Biden looked at his watch as the transfer of the bodies went on. Citing media fact checks, the former press secretary says footage shows Biden did so only after the remains had left the airport tarmac.

Complaints that Biden spoke too much about his own son were tougher to deal with, Psaki writes, particularly when the New York Times “pounced” on the story.

As it was part of her job to warn Biden about “unflattering” and “negative” stories, Psaki called him, though this instance was tougher than usual because “Beau was rarely, if ever, the focus of a negative story”.

“It was one thing to tell the president the media was planning to criticise his Covid response,” Psaki writes, “and quite another to say the media was planning to criticise the way he speaks about his son, who passed away tragically young.”

Still, she writes, Jill Biden had previously told her: “We’ve been through a lot. And we ask that you always be honest with us. Always tell us what’s coming.”

Psaki called Biden and warned him about the Times story, which would say he “referenced Beau’s death repeatedly while meeting with families of the soldiers who were killed in Afghanistan last week” and “quote a number of family members making critical comments”.

When the president finally answered her, Psaki says, he did so “in a softer voice than usual.

“I thought I was helping them. Hearing about how other people went through loss always helps me,” Biden said.

Psaki says Biden paused again, then said: “Thanks for telling me. Anything else?”

The Times story duly appeared – as did others like it.

One bereaved father, Mark Schmitz, told the Times he showed the president a picture of his son, L/Cpl Jared Schmitz, who was 20, and said: “Don’t forget his name.”

“I respect anybody that lost somebody,” Schmitz said, “but it wasn’t an appropriate time.”

Psaki also describes how she herself dealt with the controversy.

In the White House briefing room, she told reporters: “While [Biden’s] son did not lose his life directly in combat as [those killed in Kabul did] – or directly at the hands of a terrorist, as these families did … he knows firsthand there’s nothing you can say, nothing you can convey, to ease the pain and to ease what these families are going through.”

Psaki also said Biden was “deeply impacted by these family members who he met … talk[ing] about them frequently in meetings and [the] incredible service and sacrifice of their sons and daughters. That is not going to change their suffering, but I wanted to convey that still.”