McCartney posted an open letter to his website Thursday (Nov. 14) assuring Putin that the 28 activists from Greenpeace that were placed in jail last month after they staged a protest at a Russian oil-drilling platform in the Arctic Ocean are neither anti-Russia nor working on behalf of the western governments.

"In my experience they tend to annoy every government! And they never take money from any government or corporation anywhere in the world," McCartney wrote. "And above all else they are peaceful. In my experience, non-violence is an essential part of who they are."

In the letter, which takes a friendly tone and is addressed to "Vladimir," McCartney writes that the protestors do not think they are "above the law," and hopes that the President couldn't intervene and help get them released.

"They say they are willing to answer for what they actually did," McCartney writes. "So could there be a way out of this, one that benefits everybody?"