The US National Security Agency (NSA) has collected and stored almost 200 million text messages a day from around the world, UK media report.
The NSA extracts and stores data from the SMS messages, and UK spies have had access to some of the information, the Guardian and Channel 4 News say.
The reporting is based on leaks by ex-NSA contractor Edward Snowden and comes ahead of a key US policy announcement.
The NSA told the BBC the programme stored “lawfully collected SMS data”.
“The implication that NSA’s collection is arbitrary and unconstrained is false,” the NSA said.
President Barack Obama is set on Friday to announce changes to the US electronic surveillance programmes, based in part on a review of NSA activities undertaken this autumn by a White House panel.
On Thursday, the White House said Mr Obama had briefed UK Prime Minister David Cameron on the review.
Read more: BBC.co.uk