EU data regulators will carry out their own investigation into whether privacy rules have been breached by secret US surveillance programmes, according to the bloc's privacy experts.

In a letter published on Monday (19 August) to EU Justice commissioner Viviane Reding, Jacob Kohnstamm, Chairman of the Article 29 working party, said that his group would assess the controversial PRISM programme as well as other platforms used by the US National Security Agency (NSA).

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Chief among the group's wish-list were demands for precise information on what data was collected and whether there were safeguards to control access to it.

It also called for clarification on whether the US intelligence programs were in line with European and international law.

"Collection of and access by the American intelligence community to data on non-US persons are of great concern to the international data protection community,"

"The WP29 considers it is its duty to also assess independently to what extent the protection provided by EU data protection legislation is at risk and possibly breached and what the consequences of PRISM and related programs may be for the privacy of our citizens’ personal data," Kohnstamm added.

The Article 29 group, which brings together national data protection supervisors from across the 28-member bloc, advises the EU institutions on policies relating to data protection. The group said that it would also investigate whether the EU ran similar snooping programmes itself.

The letter was also sent to home affairs commissioner Cecilia Malmstrom, together with European Parliament President Martin Schultz and Juan Lopez Aguilar, who chairs the assembly's civil liberties committee.

The row briefly threatened to delay trade talks between the EU and US, before the two sides agreed to establish a working group to look into the allegations to work in parallel. The European Commission, together with officials representing the Lithuanian presidency, will represent the EU in the talks.

In a statement on Monday (19 August), Reding's spokesperson, Mina Andreeva, said that the EU executive welcomed “the strong support” for its stance from the Article 29 group.

The extent of the NSA's intelligence gathering, which included the collection of telephone records and data from the Internet, has been detailed in a series of documents leaked to the media by whistleblower Edward Snowden. The EU's own institutions were also found to have been subject to the US surveillance regime.

Meanwhile, UK authorities have sparked public outrage after detaining and interrogating the partner of a Guardian journalist who was the first to interview Snowden and publish his leaked documents.

David Miranda, a Brazilian citizen, was questioned for nine hours on Sunday at London's Heathrow airport under British anti-terrorism laws before being released without charges.

British authoritiees on Tuesday said the procedure was "legally and procedurally sound."