WASHINGTON (AFP) - The mother of executed United States reporter James Foley said she felt her son's case was an "annoyance" to the US government.

In an interview aired on Thursday with CNN, Mrs Diane Foley said her family was warned it could be charged if it tried to raise ransom money to free their son.

The family was also told no prisoners would be exchanged for Mr Foley, nor would the government take military action, the mother said. The family was told not to go to the media and "trust that it would be taken care of". "As an American I was embarrassed and appalled," Mrs Foley said.

"I think our efforts to get Jim freed were an annoyance" to the US government, she added. "It didn't seem to be in our strategic interest, if you will."

The 40-year-old freelance reporter's death was revealed Aug 19 in a video released by Islamic State of Iraq and Syria (ISIS) militants, in which he is seen being beheaded.

ISIS said his killing was in response to US air strikes against it. A week later it released another video showing the beheading of another American journalist Steven Sotloff.

Mr Foley had covered wars in Afghanistan, Libya and Syria and contributed to GlobalPost, Agence France-Presse and other outlets. He was seized by armed men in northern Syria in 2012.

"Jim would have been saddened. Jim believed to the end that his country would come to their aid," Mrs Foley said.

"We were just told to trust that he would be freed somehow, miraculously," she added. "And he wasn't, was he?"