MADRID (Reuters) - Clear rules defining green energy are necessary to tackle misleading or exaggerated climate-friendly claims, the chief executive of Spain's Iberdrola Renovables Energia said at the Future Energy Summit in Madrid on Tuesday.

"We have to be very careful with greenwashing," said Julio Castro, whose company is the renewables arm of Spain's Iberdrola.

"This is something that a renewable energy producer might not have been concerned about many years ago, but today we have to be very concerned about it," he added.

The European Commission and national authorities in the region are moving to step up efforts against misleading greenwashing practices.

Castro said clear rules should "define what is green and what is not green", based on either industry self-regulation and agreement on such criteria or on regulation imposed by regional or national authorities.

"A drop of green stuff in a bucket full of black stuff does not make it green," he said.

(Reporting by Pietro Lombardi; editing by David Latona)

By Pietro Lombardi