'A lot at stake' in US surveillance row

US spy chief James Clapper has strongly defended government surveillance programmes after revelations of phone records being collected and internet servers being tapped.

Revelations of an alleged programme to tap into servers of nine internet firms were "reprehensible", he said.

He issued a strong-worded statement late on Thursday, after the UK's Guardian newspaper said a secret court order had required phone company Verizon to hand over its records to the National Security Agency (NSA) on an "ongoing daily basis".

That report was followed by revelations in both the Washington Post and Guardian that US agencies tapped directly into the servers of nine internet firms to track people in a programme known as Prism.

The BBC's technology correspondent Mark Gregory has more details.