Human Rights Watch has accused Israel of war crimes in Gaza
A leading human rights group has rejected a claim by its founder that it is biased against Israel.
Robert Bernstein said Human Rights Watch had strayed from its original mandate to scrutinise closed societies, not democracies like Israel.
In an article in the New York Times, he said the organisation had helped to turn Israel into a pariah state.
In response, Human Rights Watch said its reporting on Israel was only a tiny fraction of its work.
The organisation has accused Israel of committing war crimes during its attack on Gaza earlier this year.
Mr Bernstein, who was chairman of Human Rights Watch from 1978 to 1998, said the group had been set up to pry open closed societies and advocate basic freedoms, and therefore had drawn a distinction between democratic and non-democratic states.
"Now the organisation, with increasing frequency, casts aside its important distinction between open and closed societies," he said.
"Nowhere is this more evident than in its work in the Middle East. The region is populated by authoritarian regimes with appalling human rights records.
"Yet in recent years Human Rights Watch has written far more condemnations of Israel for violations of international law than of any other country in the region," Mr Bernstein wrote.
He accused Human Rights Watch of losing "critical perspective" in the Middle East conflict.
"Only by returning to its founding mission and the spirit of humility that animated it can Human Rights Watch resurrect itself as a moral force in the Middle East and throughout the world," he wrote.
Human Rights Watch spokesman Carol Bogart strongly rejected the claims, saying democracies also committed abuses and had to be monitored.
She told the BBC that the group was not saying Israel shouldn't fight wars, only that it shouldn't violate international humanitarian law when it did so.
She said the group's work on Israel was only a tiny fraction of its work in the region, and the world.
Mr Bernstein's criticism of Human Rights Watch comes soon after the release of a report for the UN Human Rights Council into Israel's offensive in Gaza in December and January.
The Goldstone report says there is evidence that both Israel and Palestinian militants committed war crimes, but Israel and the US have criticised its findings and recommendations.
In the latest exchanges, lead investigator, South African jurist Richard Goldstone, challenged the US to justify its allegation that the document is flawed.
He told al-Jazeera television that he doubted whether most of his critics had actually read the 574-page report.
The text - which has been endorsed by the UN Human Rights Council - says alleged perpetrators should be referred to the International Criminal Court if Israel and the Hamas authorities in Gaza do not conduct credible investigations within six months.