Controversy has grown over using food crops to make biofuels as an alternative to fossil fuels. Some environmentalists and politicians say it has raised food prices, distorted government budgets and led to deforestation in southeast Asia and Brazil.

"We should be very, very careful about coming up with biofuel solutions that have major impact on production of food grains and may have an implication for overall food security," Pachauri, chairman of the UN's Intergovernmental Panel on Climate Change, told a news conference.

"Questions do arise about what is being done in North America, for instance to convert corn into sugar then into biofuels, into ethanol," he said.

The United States is the world's biggest producer of biofuels, derived mostly from corn.

"Several questions have arisen on even the emissions implication of that route, and the fact that this has clearly raised prices of corn," said Pachauri, whose panel shared the Nobel prize with former US Vice President Al Gore last year.

Scientists say some kinds of biofuel generate as much carbon dioxide (CO2) as the fossil fuels they replace.

Supporters, however, say biofuels are the only renewable alternative to fossil fuels and do generally result in greenhouse gas emission savings.

Pachauri, in Brussels for talks with European Union lawmakers, said it was crucial to look at other ways of producing biofuels, including investing strongly in research and development to convert cellulosic material into liquid fuels, as well as using agricultural residues.

EU leaders pledged last year to increase the proportion of biofuels used in petrol- and diesel-consuming land transport to 10 percent by 2020, but concern that this is pushing up food prices has led the bloc to say it may reconsider its strategy.

Pachauri declined to comment on this specific target but said the EU should regularly seek feedback on its impact and review it if necessary.

"I think we have to set up a system by which we get a proper feedback and evaluate it on a regular basis," he told Reuters.

Earlier this month EU leaders pledged to pass laws within 12 months to implement ambitious goals for combating climate change, including slashing greenhouse gas emissions by 20 percent by 2020 and increasing the share of renewable energy.

Pachauri commended the 27-nation bloc's efforts, saying it had taken a much needed leadership role on climate change.

Asked if countries applying strict emissions curbs to fight climate change should tax imports from countries which do not, Pachauri said he hoped this would not be necessary.

The outcome of a UN conference in Copenhagen next year meant to adopt a new climate change treaty would be instrumental in that regard, he said.