An episode of Finding Your Roots which omitted references to Ben Affleck's ancestor as a slave owner violated PBS standards, the public TV service has said.

In a statement today, PBS said it is postponing the show's third season and delaying a commitment to a fourth year until it is satisfied with improvements in the show's editorial standards.

The public TV service launched an investigation after it was reported that Affleck requested the programme not reveal that his ancestor was a slave holder in the 2014 episode. The Associated Press examined historical documents and found that the actor's great-great-great grandfather owned 24 slaves.

The review found that co-producers violated PBS standards by allowing improper influence on the show's editorial process and failed to inform PBS or producing station WNET of Affleck's efforts to affect the programme's content.

In a statement, series host and executive producer Henry Louis Gates Jr apologised for forcing PBS to defend the integrity of its programming. He said he is working with public TV on new guidelines to ensure increased transparency.

Affleck's request came to light last spring in hacked Sony emails published online by whistleblower site WikiLeaks.

"These reports marked the first time that either PBS or WNET learned of this request," PBS said today.

PBS said it will withdraw the episode from all forms of distribution including on-air, digital platforms and home video.

Gates and PBS said in April they did not censor the slave-owner details. Instead, more interesting ancestors of the actor emerged and Gates chose to highlight them instead.

But in an email exchange between Gates and Sony Pictures co-chairman and chief executive Michael Lynton, Gates asks Lynton for advice on how to handle Affleck's request.

"Here's my dilemma," says Gates in one email, dated July 22 2014 - "confidentially, for the first time, one of our guests has asked us to edit out something about one of his ancestors - the fact that he owned slaves. Now, four or five of our guests this season descend from slave owners, including (prolific documentary film-maker) Ken Burns. We've never had anyone ever try to censor or edit what we found. He's a megastar. What do we do?"

Lynton replied that it all depends on who knows that the information was in the documentary already.

Last January, PBS station WETA in Washington DC succeeded WNET as the show's producing station.