White House chief of staff John Kelly was unaware President Trump would publicly disclose that former President Barack Obama never called him after his son was killed in Afghanistan, according to a report Wednesday.

Kelly, who had privately told Trump he never received a call from former President Barack Obama after his son was killed by stepping on a landmine in Afghanistan, was surprised when Trump mentioned it in a radio interview, CNN reported.

"As far as other presidents, I don't know, you could ask Gen. Kelly, did he get a call from Obama? I don't know what Obama's policy was," Trump said during a Fox News radio interview Tuesday, in response to his claims earlier this week that Obama and other former presidents didn't make calls often to families who lost someone who served in the military.

White House press secretary Sarah Sanders said Wednesday Kelly "is disgusted by the way this has been politicized and that the focus has come on the process, and not the fact that American lives were lost. I think he is disgusted and frustrated by that."

Sanders added that Trump and Kelly have discussed the incident.

Kelly has attempted to keep his son's death private. He is the most senior military official to have lost a child in Iraq and Afghanistan.

Although Obama did not call Kelly, Obama did host Kelly and his wife at a breakfast for Gold Star families six months after their son had died.

Trump asserted he believed he has called all the families of those who lost loved ones serving the nation. But the Associated Press reported relatives of two soldiers who passed away did not receive a call or letter from the president. Additionally, a third fallen soldier's family said they did not receive a call from him, according to the report.

Four U.S. Army Special Forces were killed during an ambush of a joint patrol of U.S. and Nigerien forces along the Niger-Mali border in early October. The president faced criticism after two weeks past and he hadn't reached out to the families. The White House announced on Tuesday that Trump finally did speak over the phone with all four of the families of the soldiers killed in Niger.

At least 20 Americans have lost their lives serving the nation since January.