Peru's government said Monday that the environmental group Greenpeace hasn't given it the names of the activists officials accuse of damaging the world-renowned Nazca lines by leaving footprints in the adjacent desert during a publicity stunt.

In the protest at the U.N. World Heritage site in Peru's coastal desert, activists laid a message promoting clean energy beside the famed figure of a hummingbird comprised of black rocks on a white background. The message was directed at delegates at the U.N. climate talks being held in nearby Lima.

Peruvian officials have said they would seek charges for "attacking archaeological monuments," a crime punishable by up to six years in prison.

Culture Minister Diana Alvarez-Calderon said Monday that Peru "hasn't obtained what it would have liked to obtain: names, passports, addresses" of the activists involved.

"What Greenpeace's representative says is that they want to conduct an investigation that will last about a month because they are going to look into 27 affiliates. They want to know who produced the idea for the event, who organized it and who went to it," said Alvarez-Calderon.

Attempts to reach Greenpeace on Monday for comment were not successful. But previously the environmental group has apologized for the stunt and said it was willing to accept the consequences.

The activists entered a "strictly prohibited" area where they laid big yellow cloth letters reading: "Time for Change; The Future is Renewable." They said after initial criticism that they were "absolutely careful" not to disturb anything.

But Peruvian officials say that no one, not even presidents and Cabinet ministers, is allowed without authorization where the activists trod, and those who do have permission must wear special shoes.

The Nazca lines are huge figures depicting living creatures, stylized plants and imaginary figures scratched on the surface of the ground between 1,500 and 2,000 years ago. They are believed to have had ritual astronomical functions.