LONDON (Reuters) -

Monsanto's Roundup weedkiller atomizers are displayed for sale at a garden shop at Bonneuil-Sur-Marne near Paris, France, June 16, 2015. REUTERS/Charles Platiau

The World Health Organization’s cancer agency - which is facing criticism over how it classifies carcinogens - advised academic experts on one of its review panels not to disclose documents they were asked to release under United States freedom of information laws.

In a letter and an email seen by Reuters, officials from the International Agency for Research on Cancer (IARC) cautioned scientists who worked on a review in 2015 of the weedkiller glyphosate against releasing requested material.

The review, published in March 2015, concluded glyphosate is “probably carcinogenic,” putting IARC at odds with regulators around the world. Critics say they want the documents to find out more about how IARC reached its conclusion.

“IARC is the sole owner of such materials,” IARC told the experts. “IARC requests you and your institute not to release any (such) documents.”

Asked about its actions, the agency told Reuters on Tuesday it was seeking to protect its work from external interference and defending its panels’ freedom to debate evidence openly and critically.

In recent years IARC, a semi-autonomous unit of the WHO based in Lyon, France, has caused controversy over whether such things as coffee, mobile phones, red and processed meat, and chemicals like glyphosate cause cancer.

Its critics, including in industry, say the way IARC evaluates whether substances might be carcinogenic can cause unnecessary health scares. IARC assesses the risk of a substance being carcinogenic without taking account of typical human exposure to it.

Glyphosate is a key ingredient of the herbicide Roundup, sold by Monsanto. According to data published by IARC, glyphosate was registered in over 130 countries as of 2010 and is one of the most heavily used weedkillers in the world.

Pressure has been growing on the experts who worked on IARC’s glyphosate review in part because other regulators, including in the United States, Europe, Canada, Japan and New Zealand, say the weedkiller is unlikely to pose a cancer risk to humans.

The conflicting scientific assessments have delayed a decision on whether glyphosate should be relicensed for sale in Europe, and prompted senior U.S. lawmakers to question whether IARC should receive funding from U.S. taxpayers.

IARC defends its methods as scientifically sound and says its monographs - the name it gives to its classifications of carcinogens - are “widely respected for their scientific rigor, standardized and transparent process and . . . freedom from conflicts of interest.”

IARC’s advice to experts not to release documents came in April after IARC said it learned that members of the scientific panel that reviewed glyphosate in 2015 had been issued with legal requests for information relating to their work.

Multiple subsequent freedom of information requests by the U.S. conservative advocacy group the Energy and Environment Legal Institute (E and E Legal) have since been turned down by agencies and universities citing IARC’s reasoning that it owns the documents.

David Schnare, General Counsel of E and E Legal, told Reuters his group is now pursuing a legal challenge over whether the documents belong to IARC, or are the property of the U.S. federal and state institutions where the panel experts work.

He said E and E wants access to the documents and emails because it wants to know more about the way IARC reviews the scientific evidence, and about its relationship with the U.S. Environmental Protection Agency (EPA).

“PRIVATE EMAILS”

An email dated April 1 was addressed to six members of the working group for monograph 112, which considered glyphosate, including experts at universities in Texas and Mississippi as well as scientists attached to the EPA.

Signed and sent by Kathryn (Kate) Guyton, the IARC staffer responsible for the glyphosate review, the email said IARC “does not encourage participants to retain working drafts or documents after the monograph has been published.”

Monsanto’s vice president of strategy, Scott Partridge, told Reuters he considered IARC’s actions “ridiculous.”

“The public deserves a process that is guided by sound science, not IARC’s secret agendas,” he said.

Responding to Reuters’ questions about the letter and email, IARC said it had been previously informed by experts on the panel who “had been approached by interested parties, including lawyers representing Monsanto . . . and asked to release private emails as well as draft scientific documents.”

It said that as international agencies, both IARC and the WHO “have policies to protect their work, and the contributions of their expert Working Groups, from external interference.”

In a statement to Reuters, IARC said the letter and email were sanctioned by the agency’s director, Chris Wild. It added: “IARC staff did not instruct anyone not to comply with records requests made under national or local law.”

It said it is vital that scientists in its working groups “are able to openly and critically debate the scientific evidence.”

“IARC considers any measures that would discourage scientists from participating in Monographs or would detract from open scientific debate to be contrary to the best interests of international public health,” it added.

Ivan Rusyn, one of the recipients of the IARC’s April letter and email and a professor at Texas A and M University who worked on the glyphosate review, said he was glad to have IARC’s advice regarding whether documents should be released.

“I don’t see anything inappropriate here,” he told Reuters. “It’s very appropriate for IARC to advise its working group members as to what the procedures are.”