The widow of a dead US soldier says Donald Trump could not remember her husband's name when he phoned to offer condolences.

Myeshia Johnson, widow of Sgt La David Johnson, told ABC News the president's "stumbling" had "hurt her the most".

But President Trump said that he had used Sgt Johnson's name "without hesitation" and described the conversation as "very respectful".

Sgt Johnson was killed in Niger by Islamist militants this month.