Washington - National Security Agency chief General Keith Alexander revealed that his spy agency once tested whether it could track Americans' cellphone locations, in addition to its practice of sweeping broad information about calls made.Alexander and Director of National Intelligence James Clapper testified at a Senate Judiciary Committee hearing on proposed reforms to the NSA's surveillance of phone and internet usage around the world, exposed in June by former NSA analyst Edward Snowden. But neither spy chief discussed proposed reforms; instead they were questioned about new potential abuses that have come to light since then.Alexander denied a New York Times report published on Saturday that said NSA searched social networks of Americans searching for foreign terror connections, and detailed 12 previously revealed cases of abuse by NSA employees who used the network for unsanctioned missions like spying on a spouse. He said all employees were caught and most were disciplined.Congress is mulling changes to the Foreign Intelligence Surveillance Act that some believe allows the NSA too much freedom in gathering US data as part of spying on targets overseas.Secret courtAlexander told the committee that his agency once tested, in 2010 and 2011, whether it could track Americans' cellphone locations, but he said the NSA does not use that capability, leaving that to the FBI to build a criminal or foreign intelligence case against a suspect and track him."This may be something that is a future requirement for the country but it is not right now because when we identify a number, we give it to the FBI," Alexander said. "When they get their probable cause, they can get the locational data."He said if the NSA thought it needed to track someone that way, it would go back to the Foreign Intelligence Surveillance Court - the secret court that authorises its spying missions - for approval. He added that his agency reported the tests to both House and Senate intelligence committees, and that the data was never used for intelligence analysis.Only last week, Alexander refused to answer questions from Senator Ron Wyden, a Democrat from Oregon, about whether his agency had ever collected or planned to collect such "cell-site" data, as it is called, saying it was classified, but the general said the NSA released the information in letters to the House and Senate Intelligence Committees ahead of the Judiciary Committee meeting on Wednesday.Wyden was not satisfied with Alexander's answer.Social networks"After years of stonewalling on whether the government has ever tracked or planned to track the location of law abiding Americans through their cellphones, once again, the intelligence leadership has decided to leave most of the real story secret - even when the truth would not compromise national security," he said.Alexander acknowledged his agency collects data from social networks and other commercial databases to hunt foreign terror suspects but is not using the information to build private files on Americans. He said the operations are only used in pursuing foreign agents and sweeping up information on Americans if they are connected to those suspects by phone calls or other data.Alexander said that not all social network searches are authorised by the secret Fisa court, but he added the agency's searches are proper and audited internally. The authority flows from a presidential executive order on national security dating back to the Reagan administration in 1981, he said, adding: "It allows us to understand what the foreign nexus is."