The behind-the-scenes NSA concerns — which haven't been reported before — could be relevant as Congress decides whether to renew or modify the phone records collection when the law authorizing it expires in June.
Reports are that U.S. intelligence had recruited two Germans, a man who worked at the country's foreign intelligence agency and a defense ministry employee, are "troubling."
The German leader said her government felt responsible for protecting the privacy rights of its citizens and she would lead negotiations with Washington over a "no spy" agreement between the two countries "with the force of our arguments."
The recommendation by the Privacy and Civil Liberties Oversight Board is even more sweeping than a similar proposal from another panel of experts that advised Obama to restrict phone surveillance to limited court-ordered sweeps.
U.S. leaker Edward Snowden's revelations about the NSA's spying programs have sparked concern among politicians in countries from Latin America to Europe.
Court records from 2009 say that after repeated assurances the NSA would obey the court's rules, it acknowledged that it had collected material improperly.
The British newspaper The Guardian said Thursday that it obtained a confidential memo that suggests U.S. intelligence was able to monitor the communications of 35 world leaders in 2006.