More than 700 doctors from 43 countries have written a letter of protest to their governing ethical body, the World Medical Association, alleging that its recently appointed Israeli president has turned a blind eye to the involvement of medical staff in torture, and calling for his removal.

Dr Yoram Blachar, leader of the Israeli Medical Association since 1995, assumed the helm of the WMA in November. The signatories to the letter, who include senior doctors and professors from the UK, Europe and the US, claim he has failed to answer charges that some Israeli doctors condone or collaborate with a regime that uses torture against Palestinian prisoners.

As long ago as 1996, the letter says, Amnesty International concluded that doctors in Israel working with the security services "formed part of a system in which detainees are tortured, ill-treated and humiliated in ways that place prison medical practice in conflict with medical ethics".

The letter, whose lead signatory is the paediatrician Alan Meyers from the Boston University school of medicine, says Blachar's presidency "makes a mockery of the principles on which the WMA was founded in 1947, which was as a response to egregious abuses by German and Japanese doctors" in the second world war.

The doctors say inaction is not an option. The WMA's 1975 Declaration of Tokyo said "physicians shall not countenance, condone or participate in the practice of torture or other forms of cruel, inhuman or degrading procedures, and in all situations, including armed conflict and civil conflict". Two years ago, its annual general assembly explicitly obliged doctors to document cases of torture of which they become aware. "The absence of documenting and denouncing such acts might be considered as a form of tolerance and of non-assistance to the victims," it ruled.

In an email to the Guardian promising a response to the charges, Blachar called them "imaginary allegations which have no grounds whatsoever". He claimed that most who signed the appeal "did not bother to verify the content". No detailed rebuttal was forthcoming, however.

Meyers said Blachar had in effect defended the participation of Israeli physicians in the torture of Palestinian prisoners in Israeli jails. In a letter to the Lancet medical journal in 1997, Blachar wrote: "The guidelines on interrogation recommend that only 'moderate physical pressure' (in accordance with international law, and not unknown in other democratic countries) be sanctioned."

"As you may know," Meyers said, "'moderate physical pressure' – the same formulation employed by the Bush administration in its prisons at Guantánamo Bay and CIA 'black sites' in other countries (and now a subject of heated debate in the US) – includes confining prisoners in stress positions, beatings, isolation, sleep deprivation, extremes of heat and cold, humiliation and other forms of physical and psychological abuse.

"Physician collaboration in such maltreatment is unacceptable, and the defence of such physician participation should disqualify Dr Blachar from any position of leadership within the international physician community."

Meyers, who is Jewish, has campaigned for health and human rights in Israel for a decade, but said any physician in any country who was involved with interrogation techniques of this kind should not be practising medicine. "If they did it in the US, I'd join with anyone else in seeking to have those physicians brought to account," he said.

Further allegations of Israeli doctors' involvement in torture came in a report two years ago from the Public Committee Against Torture in Israel, which gave detailed testimony from nine Palestinian men interrogated between 2004 and 2006. Blachar's critics accuse him of failing to respond to either this report or Amnesty's evidence.

Sir Iain Chalmers, a senior British doctor, editor of the James Lind Library and a co-founder of the Cochrane Collaboration, is one of the signatories to the letter. "Previous appeals to Yoram Blachar himself, in a number of places and from a number of people, to answer factually based allegations of medical complicity in torture have not resulted in any adequate response," he said.

"The issue now is: does the WMA have any credibility as long as it continues to ignore people who are complaining about its acquiescence and support of Dr Blachar and the Israeli Medical Association?

"There have been no satisfactory responses from the IMA to allegations both by Israeli organisations and Amnesty International over the years."

Dr Derek Summerfield, of the Institute of Psychiatry at King's College London, who was the co-ordinator of the letter, said: "The appointment of the long-standing president of the IMA to lead the WMA, which is the world body overseeing medical ethics, which arose out of the abuses of the second world war, just seems to make a mockery of the whole idea that there is an ethical framework for what doctors do and what they don't do."