President Donald Trump on Monday accused Barack Obama and other past American presidents of failing to call the family members of slain service members, a claim a former Obama aide called “an outrageous and disrespectful lie.”

Four Green Berets were killed earlier this month in an ambush in Niger. But Trump has stayed publicly silent on the issue until Monday, when he was asked during a Rose Garden news conference why the American people hadn’t heard the president speak about the deaths related to the Oct. 4 attack.

“I’ve written them personal letters. They’ve been sent, or they’re going out tonight,” the president told reporters. “But they were written during the weekend. I will at some point during the period of time call the parents and the families, because I have done that traditionally.”

Trump said he feels “very, very badly about” having to make those calls and always does. “The toughest calls I have to make are the calls where this happens: soldiers are killed,” he added.