US lawyers say they have "explosive" documents about crisis-hit agribusiness giant Monsanto and their affairs in Europe.

Those involved in a successful lawsuit against the firm have been in Brussels, addressing a European Parliament special committee.

Last month, Monsanto was ordered to pay 289 million dollars to a former school groundskeeper dying of cancer, after it was agreed the firm's Roundup weedkilled contributed to his disease.

"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 Jr. Kennedy.

"And many of them are pertinent to what Monsanto did here in Europe. And that's just the beginning."

Beyond the environmental battle, what's happened also raises the issue of transparency. For one Green MEP, the US legal battle is also one for democracy.

"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's Bart Staes.

Last November, the EU approved the use of glyphosate, a chemical used in Monsanto's Roundup product, for five years after a heated debate over whether it causes cancer.