"It's a shocker," said Simon Young, a law professor with Hong Kong University. The U.S. government will be fuming with rage."

China's news agency, referring to Snowden's accusations about the hacking of Chinese targets, said they were "clearly troubling signs". It added: "They demonstrate that the United States, which has long been trying to play innocent as a victim of cyber attacks, has turned out to be the biggest villain in our age."