NHS England chief nursing officer Jane Cunningham has told ITV Daybreak that "people should not lose confidence in the [NHS 111] service."
At least 22 "possible serious untoward" incidents - including three where a patient died - relating to the new NHS 111 advice line, a health magazine reports.
The deaths are being investigated. NHS England is keeping a 'careful eye' on the service.
Ms Cunningham added: "The three individuals will clearly need to be investigated and we need to see what really happened in those cases."
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ATM machines were affected, while people also reported problems using cards in shops.