White House Deputy press secretary JoshEarnest gestures while speaking during his daily news briefing at the White House in Washington, Friday, May, 31, 2013. (AP Photo/Pablo Martinez Monsivais) White House Deputy press secretary Josh Earnest (Pablo Martinez Monsivais/AP)

White House spokesman Josh Earnest defended the administration's program of collecting the telephone records of tens of millions of Verizon customers in the U.S., calling it a "critical tool."

Speaking to reporters aboard Air Force One on Thursday, Earnest said that while he could not disclose classified information, the top-secret court order issued in April — first reported Wednesday night by the Guardian newspaper — helped alert U.S. officials to possible terrorist activities.

Earnest read a statement at the top of his part of the gaggle, about the “robust legal regime” that reviews the use of the government powers under the Patriot Act “to ensure that they comply with the Constitution.”

He declined to say whether the particular order in question today has been in place for seven years, as lawmakers have said. But Earnest did say that the “authorities that are referenced by this reported order are something that have been in place for a number of years now.”

Asked whether President Obama is comfortable with the way the law is being interpreted in his administration, Earnest referred again to the legal oversight and said “this strict regime reflects the president’s desire to strike the right balance between protecting our national security and protecting constitutional rights and civil liberties.”

Earnest declined to say whether the order relates to a specific probe, citing the fact that the material in question is classified.

Like Sen. Dianne Feinstein (D-Calif.), who confirmed the program's existence Thursday, Earnest emphasized that the court order does not allow intelligence officials to listen in on calls. Congress has been fully briefed on the matter, he added.

This post has been updated.