The Monsanto product – the world’s most widely used herbicide – contains glyphosate, which may also be carcinogenic for non-Hodgkin’s lymphoma

Roundup, the world’s most widely used weedkiller, “probably” causes cancer, the World Health Organisation (WHO) has said.

The International Agency for Research on Cancer (IARC) – WHO’s cancer agency – said that glyphosate, the active ingredient in the herbicide made by agriculture company Monsanto, was “classified as probably carcinogenic to humans”.

It also said there was “limited evidence” that glyphosate was carcinogenic in humans for non-Hodgkin’s lymphoma.

Monsanto, the world’s largest seed company, said scientific data did not support the conclusions and called on WHO to hold an urgent meeting to explain the findings. “We don’t know how IARC could reach a conclusion that is such a dramatic departure from the conclusion reached by all regulatory agencies around the globe,” said Philip Miller, Monsanto’s vice-president of global regulatory affairs.

Concerns about glyphosate on food have been widely debated in the US recently, and contributed to the passage in Vermont last year of the country’s first mandatory labelling law for genetically modified food.

The US government considers the herbicide to be safe. In 2013, Monsanto requested and received approval from the US Environmental Protection Agency for increased tolerance levels for glyphosate.

It is mainly used on crops such as corn and soybeans, which are genetically modified to survive it.

The weedkiller has been detected in food, water and in the air after it has been sprayed, according to the report from WHO. However, glyphosate use is generally low in and near homes where the general public would face the greatest risk of exposure, the report said.

The evidence for WHO’s conclusion was from studies of exposure, mostly agricultural, in the US, Canada, and Sweden that were published since 2001.