House committee questions spy chiefs about phone-tapping allegations (CNN) -- The House Intelligence Committee on Tuesday afternoon questioned U.S. spy chiefs about accusations that the National Security Agency has tapped not only the phone calls of millions of Americans, but also those of top U.S. allies. Tuesday's hearing, billed as a discussion of potential changes to the Foreign Intelligence Surveillance Act, comes amid claims, reported last week by German magazine Der Spiegel, that the NSA monitored German Chancellor Angela Merkel's cell phone. It's the latest in a series of spying allegations that stem from disclosures given to news organizations by Edward Snowden, the former NSA contractor who describes himself as a whistle-blower. Comments by President Barack Obama's administration claiming that he did not know of the practice until recently have drawn criticism from both the right and the left. Here are some highlights from the hearing: Recent assertions by European media outlets that the NSA tapped tens of millions of phone calls in Europe are "completely false," NSA chief Gen. Keith Alexander said. Media outlets misinterpreted documents that were leaked, he said, adding that the NSA legally collected metadata from some phone calls, and the rest of the metadata came from U.S. allies. To be perfectly clear, this is not information that we collected on European citizens. It represents information that we, and our NATO allies, have collected in defense of our countries and in support of military operations," Alexander said. Alexander said the NSA is working to increase transparency. "I think the greatest step in transparency that we're doing is the hiring of a civil liberties and privacy officer," he told the committee. We take this very seriously. Director of National Intelligence James Clapper said that trying to determine the intentions of foreign leaders -- by getting close to them or getting their communications -- is a "fundamental given" in the world of intelligence services, and one of the first things he learned in his intelligence career. Asked if he believes U.S. allies conducted espionage activities against U.S. leaders, he said, "absolutely." Clapper was responding to questions from House Intelligence Committee Chairman Mike Rogers during the hearing. Rogers and Rep. Adam Schiff, D-California, sparred over whether the committee knew about reported spying on foreign leaders. "I think we have a lot more work to do with you to make sure that we are getting the information that we need," Schiff said. Rogers said he was mystified by claims that the committee had been in the dark. "It is disingenuous to imply that this committee did not have a full and complete understanding of activities of the intelligence community as was directed under the national intelligence priority framework to include sources and methods," he said. Alexander vigorously defended the agency's intelligence gathering activities, saying they have saved lives "not only here but in Europe and around the world." Nothing that's been revealed about the programs "has shown that we were trying to do something illegal and unprofessional"; that if something was collected improperly, it was corrected; and that safeguards on the data collected are effective, he said. The Foreign Intelligence Surveillance Act, or FISA, "must be reformed" to improve transparency about and restore the public's confidence in the United States' intelligence gathering activities, House Intelligence Committee ranking member Dutch Ruppersberger, D-Maryland, said. Yet, the reforms must preserve the intelligence community's abilities to help protect the nation, he added. Recent leaks about U.S. intelligence gathering activities have been "extremely damaging," Clapper said in his opening remarks. He said that the intelligence community's activities have been lawful and that "rigorous oversight" has been effective. Still, he said, he is ready to work with lawmakers to "further protect our privacy and civil liberties."