Apple chief Tim Cook has spoken publicly for the first time since a row erupted with the FBI over security access to one of the San Bernardino killer's iPhones.

He told ABC News he believed he was "making the right choice" by refusing court orders to help unlock a device belonging to Syed Rizwan Farook, who with his wife, killed 14 people in California in December.

Doing so, he said, "would be bad for America" and "set a precedent that I believe many people in America would be offended by".

He said he was disappointed to find out about the court ruling from the news reports instead of the justice department, saying "something so important" should not have been "handled in this way".