Secret US surveillance of phone and internet records has thwarted dozens of potential terror attacks, the head of the National Security Agency (NSA) has said.
NSA director, General Keith Alexander's comments to Congress yesterday came on the same day a meeting between US Secretary of State John Kerry and British Foreign Secretary William Hague briefly touched on what Mr Hague called "recent controversies" during talks in Washington.
It's a week since a former NSA contractor leaked their existence to international media.
Edward Snowden had admitted to giving details of the monitoring of phone calls and internet data, from companies such as Google and Facebook, to The Guardian and Washington Post.
"It's classified, but it's dozens of terrorist events that these have helped prevent," Mr Alexander said as he was questioned on the value of the surveillance.
Mr Alexander said the thwarted attacks included "dozens for both here and abroad, in disrupting or contributing to the disruption of terrorist attacks".
Mr Alexander said his agency is working to make its actions more public to lawmakers and to US citizens.
"I want the American people to know that we're being transparent in here," he said.
Alexander insisted the NSA only obtains a warrant to look closely at data when it has "reasonable articulable suspicion".
Asked whether NSA could determine what people are looking for on the search engine Google, he said: "Yes we could. You could get a court order ... to do any kind of search in this area, you would need a court order."
Meanwhile, British Foreign Secretary William Hague acknowledged the controversy set off by the Prism programme. "The intelligence sharing relationship between the UK and the US is unique in the world, it's the strongest in the world and it contributes massively to the national security of both countries," Mr Hague said.
Mr Kerry echoed those comments, saying: "I think the Secretary and I both understand the very delicate but vital balance between privacy and the protection of people in our country."