The European Union and the United States have agreed changes to a data transfer pact that includes stricter rules for companies holding information on Europeans and clearer limits on U.S. surveillance. According to Reuters, the revised EU-U.S. Privacy Shield was sent for review by European member states. They are expected to hold a vote in early July.

Cross-border data transfers by businesses include payroll and human resources information as well as data used for targeted online advertising.

However, revelations of mass U.S. surveillance practices have caused political outrage in Europe and fuelled distrust of big U.S. tech companies such as Facebook, Google and Apple.

Last year, the EU's highest court struck down the previous system, Safe Harbour, on concerns about mass U.S. surveillance practices.

A letter from the Office of the Director of National Intelligence, seen by Reuters, gives an example of the United States seeking information on the activities of a terrorist group in the Middle East believed to be plotting attacks against Europe.

If Washington does not have information such as names, phone numbers or email addresses it would collect communications "to and from that region for further review and analysis to identify those communications that relate to the group," the letter says.

"Thus, even when targeting through the use of specific selectors is not possible, the United States does not collect all communications from all communications facilities in the world."