The UN on Friday adopted global guidelines to defend the land rights of poor farmers and recognise informal indigenous claims in a move hailed by aid groups as a step against exploitative "land grabbing".

The new voluntary rules are the result of three years of negotiations following an outcry from campaigners who accuse rich investors and developing world governments of setting up plantations that abuse human rights.

"This is extremely important," the head of the United Nations Food and Agriculture Organisation (FAO) in Rome, Jose Graziano Da Silva, told reporters.

"But today's adoption is a point of departure, not an arrival," he said, adding that implementation of the guidelines would be "a priority" for FAO.

Graziano drew attention in particular to the 40-page document's call for private companies to be transparent and consult local populations, as well as the recognition of "customary tenure systems" by indigenous populations.

FAO said in a statement that implementation of the rules would bolster global food security "by improving secure access to land, fisheries and forests and protecting the rights of millions of often very poor people."

Chief amongst the guidelines is a call on governments to "safeguard legitimate tenure rights against threats and infringements" and "provide effective and accessible means" to resolve tenure disputes.

"Non-state actors including business enterprises have a responsibility to respect human rights and legitimate tenure rights," it said.

It also called on governments to "provide appropriate recognition and protection of the legitimate tenure rights of indigenous peoples."

On the issue of expropriation, which has caused upheaval in China, the text said governments should "ensure a fair valuation and prompt compensation for farmers" and expropriate only when the land is needed for a public purpose.

Gregory Myers, an adviser to the US government's development agency USAID and head of the working group that compiled the rules said: "What remains for us is an even greater task: implementation of the guidelines."

Rights groups warn that "land grabbing" is driving up domestic food prices, forcing the eviction of local farmers and fuelling corruption.

There has been a sharp rise in such deals since the food crisis of 2008.

Experts estimate 200 million hectares (494 million acres) -- an area eight times the size of Britain -- have been bought or leased between 2000 and 2010, particularly in Africa and Asia, often to the detriment of local populations.

"The guidelines are an important step towards a more equitable and hunger-free world," Stephane Parmentier, land adviser for the international charity group Oxfam, said in a statement.

"The guidelines reaffirm the human rights of those living on the land and clearly underline the need for consultation and participation of communities affected by land investments," he said.

"However, with growing competition for natural resources and land grabbing continuing unchecked, this is no time for complacency and the guidelines must be urgently implemented," he added.

The International Land Coalition, an alliance of civil society groups, said the document was "a remarkable advance towards people-centred land governance that is firmly anchored in a human rights framework."

"Non-state actors, such as multinational corporations, are given clear responsibilities to respect human rights," it said.

Angel Strapazzon from the international farmers' movement La Via Campesina said: "It is now urgent that governments use these guidelines to adopt legislation to protect farms from this flagrant violation of their rights."

Luc Maene, chairman of the International Agri-Food Network, who represented the private sector, said: "Land tenure is fundamental to food security.

"To us in the private sector and to our farmer partners, it is important that there should be effective local administration of land registries without corruption. Fair, transparent rules benefit everyone."

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