SAN FRANCISCO: Apple chief Tim Cook went public Wednesday in his battle with the Federal Bureau of Investigation (FBI), saying that unlocking an iPhone in the name of fighting terrorism would be "bad for America."

“He equated code capable of breaking into an iPhone to a "software equivalent of cancer" that should never be unleashed on the world.

"This is not about this phone," Cook said during a television interview with ABC News.

"This is about the future. It is a precedent that should not be done in this country, or in any country."

Apple is battling the United States government over unlocking devices in at least 10 cases in addition to its high-profile dispute involving the iPhone of one of the San Bernardino attackers, court documents show.

Read: Apple ordered to hack San Bernardino shooter's iPhone

Apple has been in a legal fight with the government in the San Bernardino case, where the FBI wants the company to help hack the iPhone of Syed Farook, a US citizen, who gunned down 14 people with his Pakistani wife Tashfeen Malik in the California city in December.

When asked how he felt about Apple taking the stand with the chance information on Farook's iPhone might prevent another terrorist attack, Cook responded: "Some things are hard and some things are right. And some things are both. This is one of those things."

Cook maintained that the definite dangers of creating a way to crack into iPhone encryption trumped concerns about "something that might be there," adding he felt Apple was making the right choice.

Apple is being asked to write software that the company believes would make hundreds of millions of iPhones around the world vulnerable, according to Cook.

The only way Apple knows to get more information from Farook's iPhone would be to "write a piece of software that we view as the software equivalent of cancer; we think it is bad news to write," Cook said.

Slippery slope

He argued that the FBI demand threatens to "trample on civil liberties" and starts down a slippery slope that could lead to other court orders such as building police surveillance capabilities into devices.

"It is clear that it can be a precedent," Cook said.

"If the government can order Apple to create such a piece of software, it could be ordered for anyone else as well." Cook planned to discuss the case with US President Barack Obama, and said his company was prepared to take the matter all the way to the Supreme Court.

"We have no sympathy for terrorists," Cook said.

"We aren't protecting their privacy; we are protecting the privacy of everyone else. A physical key you could shred. A software key would stay living." He called for the case to be withdraw on the grounds that it "is bad for America."

Cook called for the clash to be settled by Congress passing law that clearly defines what private companies are required to do in such cases.

Apple engineers are already working to raise iPhone defences to a level they could not be breached in the way the government is demanding in the San Bernardino case, the New York Times reported on Wednesday, citing sources close to the company and security experts.

Google chief Sundar Pichai on Wednesday added his voice to the ranks of Silicon Valley tech firms siding with Apple.

Read: Facebook, Twitter side with Apple in encryption fight

"When you create back doors it leads to very, very bad consequences which always ends up harming users," chief executive Pichai said during a conference at Paris's Sciences Po university, as he waded into the controversy.

Meanwhile, America's top spy said in a National Public Radio interview on Wednesday that he supports the FBI's side in the high-profile battle with Apple.

Central Intelligence Agency Director John Brennan said the public would never accept criminals or terrorists having exclusive access to a physical storage box, and asked why an encrypted phone should be treated any differently.

FBI Director James Comey has explained the government's position as being about "the victims and justice" in the San Bernardino attack, whose perpetrators are believed to have been inspired by the militant Islamic State group.

"We don't want to break anyone's encryption or set a master key loose on the land," Comey said in a posting that appeared on the Lawfare blog and on the FBI website.

"The San Bernardino litigation isn't about trying to set a precedent or send any kind of message."