The US National Security Agency is ready to end later this month collecting Americans' domestic call records in bulk and move to a more targeted system, meeting a legislative deadline imposed earlier this year, according to a government memo seen by Reuters.

The memo, sent on Monday from the NSA to relevant committees in the US Congress, stated that the spy agency "has successfully developed a technical architecture to support the new programme" in time for it to become operational as scheduled on 29 November.

In stating the program's progress and the NSA's intent to use the new system, the memo appeared to rebut claims by Senate Intelligence Committee Chairman Richard Burr, a Republican security hawk, who told Reuters last week that he anticipated the new program would never be used because it was overly cumbersome and slow.

Congress passed legislation earlier this year that brought an end to the NSA's indiscriminate gathering of US phone metadata, a practice exposed by former NSA contractor Edward Snowden more than two years ago.

The legislation, known as the USA Freedom Act, called for a six-month transition period after which the NSA could only access targeted data from telephone providers with judicial approval.

"While our work is not yet complete, testing of internal systems functionality at both NSA and the telecommunications providers has begun, and exchanges of test files with the providers are under way," the NSA's memo read.

It added that it would be ready to begin the new system on 29 November and that the NSA plans to provide further updates in early 2016 about the program's implementation in addition to "a comparison between operations under [the] new program and those under the soon-to-expire bulk collection programme."

Earlier on Monday, a US federal judge ordered the NSA to stop collecting the call records of a lawyer and his firm, a narrow and largely symbolic victory for privacy advocates that does not affect the scheduled shut down of the full programme later this month.