Deadly clashes over land in Brazil constitute a reputational risk for multinational companies sourcing food from territories claimed by indigenous people, a UK-based consultancy said.

The most recent confrontation began on June 12 when indigenous activists from the Guarani-Kaiowa group set up a camp in Mato Grosso do Sul state, in a push to have their ancestral land claims formally recognised by the government.

Beef, soy and sugar are some of the products most frequently sourced from disputed lands in Brazil.

Firms buying these goods may face negative publicity from campaigners accusing them of backing "land grabs" and "violations of indigenous rights", Verisk Maplecroft senior analyst Katie Micklethwaite said.

"Mato Grosso do Sul is an obvious flash point as it has a lot of land that is lacking formal title and it's of interest to international investors," Micklethwaite told the Thomson Reuters Foundation.

"Areas with a rapidly expanding agricultural frontier and a large indigenous population are particularly at risk for land conflicts," she said late on Tuesday.

About one third of the territories claimed by Brazil's indigenous people have not been formally allocated to them through official titles, leading to frequent conflicts in some rural areas, she said.

In the most high-profile example to date, an investigation by Brazilian campaigners in 2012 found that a sugar mill in Mato Grosso do Sul had been sourcing cane from farms on land where formal titles had not been provided, despite the land being recognized as indigenous, Verisk Maplecroft said.

After the case gained international attention, multinational companies buying sugar from Mato Grosso do Sul were accused of indirectly contributing to "land grabs", Micklethwaite said.

Firms need to closely monitor their supply chains if they want to avoid these sorts of controversies and the reputational damage which comes with them, she added.