WASHINGTON (AP) — A secret U.S. global surveillance program that was revealed to the public by former National Security Agency contractor Edward Snowden has been at least temporarily halted, according to a senior congressional aide.

The NSA program, which involved the mass collection of information about phone calls, has not been used over the past six months, the aide, Luke Murry, said in a podcast interview.

Murry, a specialist in national security who works for California GOP Rep. Kevin McCarthy, did not go into detail about why the program was halted but mentioned "problems" with the way information was collected.

McCarthy's office would not comment Tuesday beyond a written statement that noted Murry was not speaking on behalf of the Trump administration when he gave the interview to the Lawfare podcast.

The White House and NSA declined comment.

The U.S. began bulk data collection of the time, length and participants — but not the content — of phone calls as part of a surveillance program started after the Sept. 11 attacks. The program prompted widespread controversy after it was publicly exposed by Snowden in 2013.

Authority for the program is due to expire this year unless Congress renews it.

Murry said in the podcast, which ran over the weekend, that he considers the collection program "critical" to national security but is not sure the administration will seek to resume it.

Oregon Sen. Ron Wyden, a Democrat who has been critical of the surveillance program, said the NSA should let the public know if it has been halted.

"The administration must permanently end the phone records program and Congress should refuse to reauthorize it later this year," Wyden said.

Despite some limits imposed by Congress, the NSA collected more than 534.4 million details of calls and text messages in 2017 from American telecom providers like AT&T and Verizon, according to the most recent government report covering NSA surveillance activities. That was more than three times the 151.2 million collected in 2016.

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Associated Press writer Deb Riechmann contributed to this report.