The US has targeted prominent human rights organisations and spied on their staff, Edward Snowden said, in giving evidence to the Council of Europe in Strasbourg, Europe's top human rights body.
Speaking via a video connection from Moscow, Snowden said that the National Security Agency - for which he worked as a contractor - had deliberately snooped on bodies like Amnesty International and Human Rights Watch.
He told members of the European Parliament: "The NSA has targeted leaders and staff members of these sorts of organisations, including domestically within the borders of the United States."
Snowden did not reveal which groups the NSA had bugged. But he gave a forensic account of how the NSA's powerful surveillance programmes violated the EU's privacy laws.
He said programmes such as XKeyscore use sophisticated data mining techniques to track "trillions" of private communications. "This technology offers the most significant new threat to civil liberties in the modern era."
XKeyscore allows analysts to search with no prior authorisation through vast databases containing e-mails, online chats and the browsing histories of millions of individuals.
The Council of Europe invited the White House to give evidence but it declined.
The EU body said: "Snowden has triggered a massive public debate on privacy in the internet age. We hope to ask him what his revelations mean for ordinary users and how they should protect their privacy and what kind of restrictions Europe should impose on state surveillance.''