European political leaders on Monday denounced US Prism surveillance operations, which tracked internet and telephone data from citizens around the world, as unacceptable and demanded more details from President Barack Obama about the nature of the programme.

The scandal was revealed by former CIA operative turned whistleblower Edward Snowden, 29, and have triggered what The Guardian – the newspaper to first break the story – described as “one of the most explosive national security leaks in US history.”

German Chancellor Angela Merkel vowed to press Obama for details of the programme at a Berlin summit next week, while European Commission Vice President Viviane Reding said she would demand clarification from US officials at a meeting in Dublin on Friday.