Four of the biggest companies involved in Brazilian cattle farming have joined forces to stop the purchase of cattle from newly deforested areas of the Amazon.

Meat companies Marfrig, Bertin, JBS-Friboi and Minerva yesterday signed a formal moratorium in which they pledge better protection for the rainforest.

The move follows a three-year Greenpeace investigation, reported extensively in the Guardian in June, which exposed the link between forest destruction and the expansion of cattle ranching in the Amazon. The investigation prompted calls for action from key international companies, including food group Princes and footwear manufacturers Clarkes, Adidas, Nike, and Timberland, which threatened to cancel contracts unless their beef and leather products were guaranteed free from raw materials linked to Amazon destruction.

John Sauven, head of Greenpeace, said: "Today's announcement is a significant victory in the fight to protect the Amazon. Cattle ranching is the single biggest cause of deforestation globally, and the fact that these multibillion dollar companies have committed to cleaning up their supply chains will lead to real change in the Amazon."

He added: "British companies have helped make this happen by getting tough with their suppliers, but this is not the end of the story. We now need to make sure that this agreement is properly enforced and extended to the entire cattle industry in Brazil."

Blairo Maggi, governor of the Brazilian state of Mato Grosso, which has the highest rate of deforestation in the Amazon and the largest cattle herd in Brazil, attended the signing in São Paulo. Maggi has announced the state will support efforts to protect the Amazon and will provide high-resolution satellite images to monitor the area.

Clearing tropical forests for agriculture is estimated to produce 17% of the world's greenhouse gas emissions - more than the global transport system.

The Greenpeace investigation compiled government records, company documents and trade data from Brazil, China, Europe, Vietnam and the US to piece together the global movement of meat, leather and cosmetics ingredients made from Brazilian cattle.