Apple's general counsel told a congressional panel on 1 March, that a court order forcing Apple to give the FBI data from an iPhone used by one of the San Bernardino shooters could threaten security on all iPhones.

"The tool that we're being asked to create will work on any iPhone that is in use today. It is extensible," Apple General Counsel Bruce Sewell told members of the US House Judiciary Committee.

"The notion that this is something only about opening one lock or that there is some degree of locks that can't be opened with the tool that they're asking us to create, is a misnomer," Sewell added.

Tuesday's testimony from FBI Director James Comey and remarks before the same US House Judiciary Committee by Sewell, brought to Congress a public fight between Apple and the government over the duelling interests of privacy and security that has so far only been heard in the courts. On 16 February, a federal court in California instructed Apple to write special software to unlock the iPhone 5c used by San Bernardino gunman Syed Rizwan Farook, an order the company is contesting.

Sewell and Comey's remarks also clarified some areas where the two sides fundamentally disagree. Comey said the tool created for Farook's iPhone would not work on other models. But Sewell said the tool that Apple was being asked to create would work on any iPhone. Sewell also responded to suggestions that Apple was addressing the encryption issue as a business issue and not a security problem.

"Every time I hear this my blood boils. But this is not a marketing issue. That's a way of demeaning the other side of the argument. We don't put up billboards that talk about our security. We don't take out ads that market our encryption. We're doing this because we think that protecting security and the privacy of hundreds of millions of iPhone users is the right thing to do," he said.

Farook and his wife, Tashfeen Malik, shot and killed 14 people and wounded 22 others in San Bernardino on 2 December 2015 before they were themselves killed in a shootout with police. The government has said the attack was inspired by Islamist militants and the FBI wants to read the phone's data to investigate any links with militant groups.