By Carey Gillam

(Reuters) - Monsanto Co, whose Roundup product is one of the world's most widely used herbicides, said on Tuesday it has arranged for an outside scientific review of a World Health Organization finding that the weed killer's key ingredient probably causes cancer.

The WHO's International Agency for Research on Cancer (IARC) said in March that it had concluded that the ingredient, called glyphosate, was probably carcinogenic after reviewing a range of scientific literature. [ID:nL2N0WM2I4]

Monsanto reacted to the finding by demanding a retraction, labeling the findings by a team of international cancer scientists as "junk science." [ID:nL2N0WP0UM]

On Tuesday, Monsanto said it had hired Intertek Scientific & Regulatory Consultancy to convene a panel of internationally recognized scientific experts to review IARC's work. The experts include medical doctors, cancer experts, and individuals with doctoral degrees who are specialists in public health, the Creve Coeur, Missouri-based company said.

Monsanto President Brett Begemann said his company is confident in the safety of its herbicide products, and the review is being done primarily to reassure consumers and others.

"It has created a lot of confusion," Begemann said of the IARC cancer link finding. "This panel is going to review the data thoroughly, and they are going to make their findings available to everyone for review."

Monsanto said the process and the findings will be independent and will be transparent. But the company said it would be involved in providing information and data for the review.

Farmers have been using glyphosate in increasing quantities since Monsanto in the mid-1990s introduced crops genetically engineered to withstand being sprayed with Roundup.

Genetically modified corn, soybeans and other crops branded as "Roundup Ready" are popular because of the ease with which farmers have been able to kill weeds. But weeds have developed resistance to glyphosate, prompting farmers to use more herbicide.

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Agricultural use of glyphosate in 2012, the most recent year for which data is available, was more than 283 million pounds (128 million kg), up from 110 million pounds (50 million kg), in 2002, according to U.S. Geological Survey estimates.

The United States and other international regulatory bodies have said glyphosate is safe when used as directed. But the WHO cancer research unit's report found that several studies have raised concerns about glyphosate and its health impacts.

(Reporting By Carey Gillam in Kansas City; Editing by Chizu Nomiyama and Jonathan Oatis)