The National Security Agency is deleting more than 685 million call records the government obtained from telecommunications companies since 2015.
That is raising questions about the viability of the programme.
After former NSA contractor Edward Snowden leaked documents revealing extensive government surveillance, Congress passed a law in 2015 that ended the NSA's bulk collection of call records. The law said future data would be retained by telecommunications companies, not the NSA, but said the intelligence agency could request information from the massive database.
Now the NSA is deleting all the information it collected from the queries because of "technical irregularities." A former top national security official at the Justice Department, David Kris, says that points to a failure of the programme.