"Europe should not extradite those accused of non-violent crimes to a court system so unfair - and prison system so cruel - that native-born defendants would rather die than become subject to it. Julian Assange could be next. Until the system is reformed, a moratorium should remain," Snowden said on Twitter.

Earlier, the El Pais newspaper reported that McAfee, 75, was found dead on Wednesday, in his prison cell in Spain's Barcelona where he committed suicide. Doctors tried to resuscitate him, but were unable to save him. McAfee's death came after the Spanish National Court approved his extradition to the United States, where he was accused of tax evasion.