US authorities have launched a probe into possible phone hacking of September 11, 2001 victims by News Corp. journalists, victims' relatives have been told, according to a Justice Department official.

During a 75-minute "initial" meeting with about 10 people whose relatives died during the terrorist attacks in New York, US Attorney General Eric Holder "broke protocol by acknowledging there is an investigation," said an attorney for the victims' families, Norman Siegel.

Holder "listened to their questions, told them the department was taking the allegations seriously, that the allegations were disturbing," said the Justice Department official who confirmed a probe into the affair was running and was in a "preliminary stage."

The official asked not to be named because they were not authorized to speak publicly about an active investigation.

"Hopefully the allegations turn out to be not true because if it's true, it's only more pain for 9/11 families," said Siegel.

"If it happens to be true... the allegation is illegal both criminally and civilly... (which brings) up to 5 years of prison and punitive damages," he added.

Siegel said the families are not accusing News Corp. of "any wrongdoing," but he added it is "logical" to ask about what happened in the United States after revelations that reporters from the media group hacked into phones in Britain.

Diane Horning, whose son was killed in the attacks said even an unsuccessful attempt to hack into the phones should be punished.

"The attempt to invade this privacy is reprehensible and will be treated even if this attempt was not successful," said Horning.

News Corp. has been shaken up by a phone hacking and corruption scandal in Britain that erupted into a full-blown crisis for the Rupert Murdoch's media empire in July and caused the media titan to close their Sunday tabloid News of the World.