The report didn't outright oppose large land transactions, reported both in Africa and Latin America but called for "fairer deals" to ensure better opportunities for African farming communities marginalized by the transactions.
Hundreds of millions of dollars of international investor funds, including hedge and pension funds, are known to have gone into the massive land deals on the two continents.
Unless properly managed, large-scale land acquisitions by foreign governments and firms could trigger "xenophobia, riots, coups and more hunger," the report warned.
The report was published by the Worldwatch Institute, which has headquarters in Washington, and follows similar warnings by the Genetic Resources Action International, Oxfam, the Oakland Institute, the World Bank and U.N. agencies.
"Deals that focus solely on financial profit can leave rural populations more vulnerable and without land, employment opportunities or food security," said the report.
"Investors claim that land grabs can help alleviate the world food crisis by tapping into a country's 'unused' agricultural potential," said Danielle Nierenberg, director of the Worldwatch Nourishing the Planet project. "But such investments often do more harm than good, disrupting traditional land-use patterns and leaving small-scale farmers vulnerable to exploitation."
The trend has accelerated as countries that lack sufficient fertile land to meet their own food needs, such as wealthier countries in the Middle East and Asia, particularly China, have turned to new fields in which to plant crops, she said.
Growing demand and rising prices for food are leading some wealthier developing countries to seek secure access to food-producing land in the territory of lower-income ones," said Worldwatch Executive Director Robert Engelman.
"If all governments capably represented the interests of their citizens, these cash-for-cropland deals might improve prosperity and food security for both sides. But that's not often the case. It's critical that international institutions monitor these arrangements and find ways to block those that are one-sided or benefit only the wealthy."
About 15 million-20 million hectares of farmland changed hands in deals or proposed deals involving foreigners from 2006 to mid-2009, the International Food Policy Research Institute reported.
Additional land acquisitions occurred in 2010, including deals in Ethiopia and Sudan, said Andrew Rice, author of "The Teeth May Smile But the Heart Does Not Forget" and contributing author to the "State of the World 2011: Innovations that Nourish the Planet" report.
Worldwatch researchers traveled to 25 countries across sub-Saharan Africa to meet with more than 350 farmers' groups, non-governmental organizations, government agencies and scientists.
Critics of large-scale land acquisitions believe the land grabs are marginalizing the land rights of indigenous populations and compromising food security in the host countries.
"(Critics) predict that the outcome will not be development but a litany of dire possible consequences: xenophobia, riots, coups and more hunger," Rice said.
Analysts said all recent reporting on land grabs pointed to a developing problem but also highlighted a bigger problem: no effective framework exists to prevent it from happening.
In fact, defenders of the vast land deals have come from the World Bank and other U.N. agencies, arguing the deals provide poor countries with money, infrastructure, resources and increases in food security.
Critics reject those arguments and warn the land grabs are accumulating huge political and security problems for both people and countries where they are concentrated.
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