Gartner has warned that multinational businesses should "re-examine the risks" of using US service providers in light of claims that leading telcos divulged millions of phone records to the US National Security Agency (NSA).

The analyst firm's warning comes after USA Today reported that three leading telecoms providers - AT &T, BellSouth and Verizon - had secretly provided the NSA with records of millions of domestic telephone calls placed in the US.

The NSA has neither confirmed nor denied the report. AT&T has not confirmed or dismissed the claims, while BellSouth stated on 15 May that it has "not provided bulk customer calling records to the NSA".

Verizon said on 16 May that it has "not provided customer records or call data" to the NSA.

Arabella Hallawell, a research vice president at Gartner, noted that divulging customers' telephone records, seemingly without court orders or other legal authorisation, raises serious questions about risk exposure for businesses that use US service providers.

"Whether or not these reports are determined to be factual, businesses with domestic and international employees and customers, particularly those with significant operations in Canada and the EU, should expect heightened sensitivity about the way they use telecoms, internet and other communications service providers in the US, and be prepared to answer questions about their use of US providers," she said.

"Providers' responses to requests from government bodies can vary widely. Qwest, for example, has stated that it refused an NSA request for customer records, and in a separate case, Google successfully fought to narrow a US federal government request for large amounts of user search data."

Hallawell added that data interception and monitoring practices, and their impact on personal privacy, have become "extremely controversial" issues.