Two journalists with access to a secret transcript of comments by Bradley Manning, the US soldier accused of leaking confidential material to whistleblowing website WikiLeaks, have denied speculation that the material could potentially help a prosecution against Julian Assange.

The pair, from Wired magazine, said there was nothing "newsworthy" in unpublished internet chat logs between Manning and Adrian Lamo, a former hacker who claims to have discussed the leak with the young intelligence officer and later tipped off the FBI.

Wired.com claimed a scoop in June when it obtained a transcript of the chats and published excerpts in which Manning, 23, appeared to confess to being the source of classified material handed to WikiLeaks, which was founded by Assange.

However, in recent days the journalists have found themselves at the centre of an increasingly acrimonious spat with critics who accuse them of withholding crucial information about the largest leak of military data in history.

The dispute has centred on the 75% of the transcript Wired has not published, claiming the information would infringe Manning's privacy or compromise sensitive military information.

Amid reports that federal prosecutors want to establish that Assange "encouraged or helped" Manning to leak the material in order to make him a co-conspirator, Wired has found itself under pressure to reveal more about the unpublished chats.

Over the past month, Lamo has made fresh claims about the soldier's relationship with Assange.

Suggesting that Assange was more than a passive recipient of the leaks, Lamo has claimed that WikiLeaks either provided Manning with a special FTP server to prioritise his leak or arranged a physical drop-off in the United States. But he admits his claims are based on memory, as the hard drive that contained his copy of the full chat transcript was taken by the FBI. Apart from US law officials, the Wired journalists are the only individuals known to have copies of the full chat.

"The chats Wired has but is withholding – and about which they are refusing to comment – are newsworthy in the extreme," Glenn Greenwald, one of Wired's fiercest critics, wrote on Monday.

The following day Evan Hansen, editor-in-chief of Wired.com, and Kevin Poulsen, the journalist who obtained the web chats, published a response to what they said were Greenwald's personal and unfounded attacks. Today both told the Guardian they had reviewed the unpublished transcripts in the last 24 hours. They concluded there was no discussion shedding new light on the relationship between Manning and Assange.

"If I were a prosecutor, everything I would be looking at [in seeking to mount a case against Manning or Assange] would be in the published record," Hansen said. "We're trying to get the news out there that is relevant to the public. If there was something like that in the unpublished [chat logs] we would have made that public six months ago."

Poulsen also said that there was nothing "newsworthy" in the parts of the transcript they had decided to hold back, adding that nothing "of substance" about Manning's relationship with Assange had been kept secret.

"We have discussions in the newsroom, at every major turn in the Manning case, about whether it is now appropriate to publish the complete logs," he said. "And so far we have concluded it isn't."

Assange is fighting extradition to Sweden, where he faces unrelated allegations – which he denies – of sexual misconduct with two women. Although there is no evidence of an imminent indictment from the US. Assange has said his greatest fear is extradition to the US, where he believes federal prosecutors are "trying to strike a plea deal" with Manning so that he can be charged as a co-conspirator.

The material allegedly leaked by Manning is said to include more than 250,000 confidential diplomatic cables; redacted versions of a selection of these have been published by the Guardian and other media outlets over the last two months.

• This article was amended on 3 January 2011, to clarify that a segment of the leaked material has been published, rather than the entire body of material.