(Corrects 'refuted' to 'challenged' in first paragraph)
LONDON, Oct 5 (Reuters) - Britain's national cyber security agency said on Friday it had no reason to doubt the assessments made by Apple and Amazon that challenged a Bloomberg story that their systems contained malicious computer chips inserted by Chinese intelligence.
Bloomberg Businessweek on Thursday cited 17 unnamed intelligence and company sources as saying that Chinese spies had placed computer chips inside equipment used by around 30 companies, as well as multiple U.S. government agencies, which would give Beijing secret access to internal networks.
"We are aware of the media reports but at this stage have no reason to doubt the detailed assessments made by AWS and Apple," said the National Cyber Security Centre, a unit of Britain's eavesdropping agency, GCHQ.
"The NCSC engages confidentially with security researchers and urges anybody with credible intelligence about these reports to contact us,” it said. (Reporting by Guy Faulconbridge and Mark Hosenball; editing by Sarah Young)