Humanitarian charities, an Israeli prime minister and a European Union commissioner were among 1,000 targets on a surveillance list drawn up by British and American intelligence agencies, it has been reported.
Unicef and Medecins du Monde were among the organisations listed in the latest batch of secret documents leaked by fugitive Edward Snowden to be published by the Guardian.
According to the newspaper, the papers reveal that British listening post GCHQ had Joaquin Almunia, vice-president of the European Commission with responsibility for competition policy, in its sights.
The revelation appears to have strained diplomatic relations, prompting an angry response from the European Commission, which issued a statement saying the claims "deserve our strongest condemnation" if proved true.
"This is not the type of behaviour that we expect from strategic partners, let alone from our own member states," it said.
Among documents dating back to January 2009 is an email address listed as belonging to the "Israeli prime minister", then Ehud Olmert. Also being targeted was an account understood to have been used to send messages between the then Israeli defence minister, Ehud Barak, and his chief of staff, Yoni Koren.
Other targets include the UN development programme and German government building as well as African heads of state and their family members, according to the newspaper.
Leigh Daynes, an executive director of Medecins du Monde in the UK, told the Guardian he was "shocked and surprised by these appalling allegations of secret surveillance on our humanitarian operations".
"We are an independent health charity delivering impartial care in some of the poorest places, including war zones.
"There is absolutely no reason for our operations to be secretly monitored. Like other humanitarian actors, we adhere strictly to the fundamental principles of independence, neutrality and impartiality in our work."
Nick Pickles, director of campaign group Big Brother Watch, said: "Yet again we are faced with widespread surveillance that has nothing to do with national security, begging the question whether GCHQ has become a law unto itself.
"If European officials are fair game it of course begs the question if British people serving in international organisations have been targeted by GCHQ.