Three members of the UN fact-finding mission on the Gaza war of 2008-09 have turned on the fourth member and chair of the group, Richard Goldstone, accusing him in all but name of misrepresenting facts in order to cast doubt on the credibility of their joint report.

In a statement to the Guardian, the three experts in international law are strongly critical of Goldstone's dramatic change of heart expressed in a Washington Post commentary earlier this month. Goldstone wrote that he regretted aspects of the report that bears his name, especially the suggestion that Israel had potentially committed war crimes by targeting civilian Palestinians in the three-week conflict.

The three members – the Pakistani human rights lawyer Hina Jilani; Christine Chinkin, professor of international law at the London School of Economics; and former Irish peace-keeper Desmond Travers – have until this moment kept their silence over Goldstone's bombshell remarks. But their response now is devastating.

Though they do not mention Goldstone by name, they shoot down several of the main contentions in his article and imply that he has bowed to intense political pressure.

They write that they cannot leave "aspersions cast on the findings of the [Goldstone] report unchallenged", adding that those aspersions have "misrepresented facts in an attempt to delegitimise the findings and to cast doubts on its credibility".

In their most stinging criticism, the three joint authors say that "calls to reconsider or even retract the report, as well as attempts at misrepresenting its nature and purpose, disregard the rights of victims, Palestinians and Israeli, to truth and justice". They point to the "personal attacks and the extraordinary pressure placed on members of the fact-finding mission", adding that "had we given in to pressures from any quarter to sanitise our conclusions, we would be doing a serious injustice to the hundreds of innocent civilians killed during the Gaza conflict, the thousands injured, and the hundreds of thousands whose lives continue to be deeply affected by the conflict and the blockade".

The four-person fact-finding mission was set up to look into allegations of war crimes committed by both Israel and Hamas during the war in which 1,400 Palestinians – at least half of whom were civilians – and 13 Israelis died. The Goldstone report concluded that some Israelis could be held individually criminally responsible for potential war crimes.

In his Washington Post article, Goldstone said evidence had since come to light as a result of subsequent Israeli military investigations into the conflict that showed that Israel had not targeted civilians as a matter of policy. Had he known that then, "the Goldstone report would have been a different document," he wrote.

Goldstone's apparent retraction of key elements of the fact-finding mission he led was seized upon with delight by the Israeli government which called for the report to be set aside in the light of his comments. An Israeli minister claimed that Goldstone had himself promised to work to have his own report "nullified".

But his three fellow members of the mission state that they "firmly stand by" the conclusions of the report. They say that neither Israel nor Hamas has come up with any convincing evidence contradicting the findings.

The three authors cite the final UN report into the Gaza war, written by a follow-up committee led by Judge Mary McGowan Davies, that criticised Israel for the slow pace with which it conducted its investigations and for its refusal to address some of the most serious allegations about its conduct. "The mechanisms that are being used by the Israeli authorities to investigate the incidents are proving inadequate to genuinely ascertain the facts and any ensuing legal responsibility."

The statement of Jilani, Chinkin and Travers will set back any attempt by Israel to have the Goldstone report revoked. The UN human rights council, which commissioned the fact-finding mission, has already made clear that the report could only be withdrawn if all four of its authors unanimously made a formal written complaint or if the UN general assembly or human rights council voted to drop it.

The Palestinian Authority (PA) welcomed the statement from the three members of the mission. "[It is] as an important reminder of what matters – that the truth must be established and justice done. It is very disturbing that members of the committee say they have been put under pressure to sanitise their conclusions," said PA spokesman Ghassan Khatib.

"Israel must not be allowed to influence the outcome of what needs to be an objective process. Nor must Israel be allowed to investigate its own actions and find itself not guilty. We pay tribute to those members of the committee who have the courage to resist Israeli pressure and insist that justice must be done."

The Israeli government responded to the latest developments by restating its view that the Goldstone report was flawed from the outset.

"Israel's position on the Goldstone report and the whole process that established the committee has not changed. The establishment of the committee was based on fundamental flaws of the United Nations human rights council. The report was handled in a highly politicised manner by a council lacking in moral authority," said Yigal Palmor, spokesman for the Israeli ministry of foreign affairs.

"We believed that the methodology, workings and findings of the committee were mind-bogglingly distorted. All this is still valid as is Israel's commitment to investigate itself regardless of resolutions by any foreign body. We believe that our investigations and our transparency in carrying those out are the best reproach to any criticisms of Operation Cast Lead."