The CEO of Spain's Iberdrola said Tuesday at the Future Energy Summit in Madrid that clear rules defining green energy are needed to counter misleading or exaggerated claims about its climate friendliness.

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

"This is something that a renewable energy producer may 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 stepping up their efforts against misleading greenwashing practices.

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

"A little 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; Spanish editing by Mireia Merino)