Environmental group Greenpeace has criticized Apple and Amazon for the inefficient use of energy at their cloud computing service U.S. data centers.

Greenpeace released a report Tuesday on how energy-efficient and "green" cloud computing is.

Apple and Amazon were singled out by Greenpeace as having some of the "dirtiest" clouds in the industry in terms of energy use, venturebeat.com reported.

The report was released to coincide with a Greenpeace ad campaign aimed at cleaning up the cloud and naming Apple, Microsoft, and Amazon as energy offenders, venturebeat.com said.

In its report Greenpeace said, "If the cloud were a country, it would have the fifth-largest electricity demand in the world," based on the fact that in 2007, the combined electricity demand of the cloud was around 623 billion kilowatt hours, beating out India, Germany and Canada in terms of total energy demand.

Apple responded to the report by saying Greenpeace's numbers were flawed and its Maiden, N.C., data center operates with much less electricity than Greenpeace reported.