NEW YORK (AFP) - The CBS television network admitted it had been mistaken in using documents whose authenticity could not be verified in a report questioning President George W. Bush`s Vietnam era military service.
"Based on what we now know, CBS News cannot prove that the documents are authentic, which is the only acceptable journalistic standard to justify using them in the report," CBS News President Andrew Heyward said in a statement.
"We should not have used them. That was a mistake, which we deeply regret," he added.
The statement is a major embarrassment for the network, which for the past week had sought to stand by the report, despite growing pressure to admit it may have been misled as to the documents` provenance.
The memos -- allegedly written by late lieutenant colonel Jerry Killian, Bush`s commanding officer in the Texas National Guard in the 1970s -- suggested political pressure was being exerted to "sugar coat" the future president`s service record.
The "60 Minutes" report also charged that Bush`s family connections had secured his assignment to the National Guard unit -- a posting that effectively spared him active duty in Vietnam.
Soon after the report aired, questions were raised over the authenticity of the memos, with numerous experts arguing the typeface could have been produced only by a modern-day word processor, not Vietnam War-era typewriters.
Heyward insisted that "60 Minutes" had "full confidence" in the original report at the time of its broadcast.
However, further forensic investigation, as well as interviews with Killian`s former secretary Marian Carr Knox and retired National Guard lieutenant Bill Burkett, who provided the documents, had challenged those earlier assumptions, he said.
In his interview to be broadcast Monday evening, Burkett admits that he deliberately misled the CBS News producer working on the report, giving her a false account of the documents` origins to protect a promise of confidentiality to the actual source.
Burkett originally said he obtained the documents from another former Guardsman.
"Now he says he got them from a different source whose connection to the documents and identity CBS News has been unable to verify to this point," CBS said.
The network said it was commissioning an independent review of the process by which the report was prepared and broadcast to help determine "what actions need to be taken."
The controversy is a personal blow to the credibility of veteran CBS anchor Dan Rather, who presented the original report and was combative in its defence when questions were first raised.
In a separate statement Monday, Rather apologised for what he described as "a mistake in judgement."
"For that I am sorry," he said. "It was an error that was made, however, in good faith and in the spirit of trying to carry on a CBS News tradition of investigative reporting without fear or favouritism."
Bush referred to the documentation row for the first time in an interview Saturday with a local newspaper in New Hampshire.
"There are a lot of questions about the documents and they need to be answered," Bush said. "I think what needs to happen is people need to take a look at the documents, how they were created, and let the truth come out."
The service records of Bush and his Democratic challenger Senator John Kerry more than 30 years ago have become a volatile issue ahead of November`s presidential election, with both candidates seeking to portray themselves as more qualified to lead the country in the war on terror.
Kerry`s campaign has had to fend off an advertising campaign by a pro-Republican group claiming that the senator`s heroism under fire in Vietnam, for which he was decorated, had been over-exaggerated at best.
A pro-Democrat group responded with an ad suggesting that Bush had failed to fulfill his National Guard service requirements.