German Chancellor Angela Merkel has called for tougher European data protection rules, following revelations about the United States' online surveillance programmes.

Ms Merkel said Germany wanted the rules to apply throughout the EU instead of being different in every country.

She also said internet companies such as Google and Facebook should be made to disclose "who they are giving data to".

"We have a great data protection law. But if Facebook is registered in Ireland, then Irish law is valid, and therefore we need unified European rules," she said.

"Germany will take a strict position," Ms Merkel added.

Last month, US officials confirmed the existence of an electronic spying operation codenamed PRISM.

Former US spy agency contractor Edward Snowden said it collects data from European and other users of Google, Facebook, Skype and other US companies.

In a separate leak, the US was accused of eavesdropping on EU and German offices and officials.

"I expect a clear commitment from the US government that in future they will stick to German law," Ms Merkel said.