Lawyers involved in a California lawsuit against Monsanto claim to have "explosive" documents concerning the Bayer-owned agrochemical giant's activities in Europe, according to Euronews.

"What we have is the tip of the iceberg. And in fact we have documents now in our possession, several hundreds documents, that have not been declassified and some of those are explosive," said US lawyer Robert Kennedy Jr, adding "And many of them are pertinent to what Monsanto did here in Europe. And that's just the beginning."

Monsanto - bought by Germany's Bayer AG in June for $66 billion, was ordered in August to pay a historic $289 million to a former school groundskeeper, Dewayne Johnson, who said Monsanto's Roundup weedkiller gave him terminal cancer. Monsanto says it will appeal the verdict.

Environmental lawyers have been in Brussels in order to address a European Parliament special committee on the issue.

"They are fighting a fight for more democracy and for transparency and to get a better insight in how big corporation such as Monsanto act and try to manipulate the facts," said Belgium MEP Bart Staes.

Last November EU approved the use of glyphosate - a key chemical in Roundup, following five years of heated debate over whether it causes cancer. While it was approved for just five years until 2022 vs. the usual 15 years, there are now rumors that they will withdraw Roundup's license this year altogether.

Labeled a carcinogen by the EPA in 1985, the agency reversed its stance on glyphosate in 1991. The World Health Organization's cancer research agency, however, classified the compound as "probably carcinogenic to humans" in 2015. California, meanwhile, has the chemical listed in its Proposition 65 registry of chemicals known to cause cancer.