Apple will resist a court order that stipulated the company must help the FBI break into a phone that belongs to one of the San Bernardino killers because it would set a "dangerous precedent".

CEO Tim Cook posted a strong response on the company's website, less than 24-hours after a US judge ruled that Apple must provide "reasonable technical assistance" to agents attempting to access data on Syed Farook's iPhone 5C - including bypassing the auto-delete feature and password protection.

If Apple were to assist the FBI, it could lead to the creation of a 'backdoor' into millions of iPhones worldwide, Mr Cook fears.

“The US government has asked us for something we simply do not have, and something we consider too dangerous to create,” said Cook.

He wrote:

“The government suggests this tool could only be used once, on one phone. But that’s simply not true.

Once created, the technique could be used over and over again, on any number of devices."

In the physical world, it would be the equivalent of a master key, capable of opening hundreds of millions of locks — from restaurants and banks to stores and homes. No reasonable person would find that acceptable.”

The tech giant has long opposed anti-encryption campaigns, and recently criticised the British government for its Investigatory Powers Bill, saying that it could hurt "hurt law-abiding citizens".

Syed Rizwan Farook, 28, and Tashfeen Malik, 27, killed 14 people and injured 21 others in an attack on an office Christmas party in the city of San Bernadino. Many of the victims were food inspector Farook's colleagues.