WASHINGTON — The National Security Agency vacuumed up more than 534 million records of phone calls and text messages from American telecommunications providers like AT&T and Verizon last year — more than three times what it collected in 2016, a new report revealed on Friday.

Intelligence analysts are also more frequently searching for information about Americans within the agency’s expanding collection of so-called call detail records — telecom metadata logging who contacted whom and when, but not the contents of what they said.

The new report — an annual set of surveillance-related statistics issued by the Office of the Director of National Intelligence — did not explain why the number of records increased so dramatically. But in an interview, Alex Joel, the office’s chief civil liberties officer, said the N.S.A. had not reinterpreted its legal authorities to change the way it collects such data.

He cited a variety of factors that might have contributed to the increase, potentially including changes in the amount of historical data companies are choosing to keep, the number of phone accounts used by each target and changes to how the telecommunications industry creates records based on constantly shifting technology and practices.