Apple says it did not know the UK was working on a "hybrid" version of the NHS coronavirus contact-tracing app using tech it developed with Google.
The firm took the unusual step of saying it was also unaware of an issue regarding distance-measuring, which was flagged by Health Secretary Matt Hancock in Thursday's daily briefing.
Apple said it was "difficult to understand" the claims.
Downing Street said the government had "worked closely with Apple and Google".