The chief executive of Google and the founder of WhatsApp, the Facebook-owned messaging service, have voiced their support for Apple in its fight with the FBI over encryption.

Apple has said it would challenge a federal court order to unblock an iPhone, used by one of the San Bernardino shooters inovled in a mass shooting on December 2nd, as the FBI tries to investigate their links to Isis militants.

Tim Cook, Apple's chief executive, has condemned the bureau's demand to remove security features and write new operating system software, saying it was "an over-reach by the US government" with "chilling implications" on customer privacy and security.

Mr Cook’s tough stance won plaudits from privacy campaigners but Apple’s peers and rivals in Silicon Valley initially remained silent on the issue.

Jan Koum, the co-founder of WhatsApp and a Facebook board member, was the first Silicon Valley executive to speak up in approval of Apple's position. In a Facebook post, Mr Koum said he "couldn't agree more with everything said in [Apple's] customer letter today".

“We must not allow this dangerous precedent to be set. Today our freedom and our liberty is at stake,” Mr Koum wrote. Facebook itself has not commented on Apple’s stance.

Later on Wednesday afternoon, Sundar Pichai, chief executive of Alphabet subsidiary Google, also spoke up, calling Mr Cook’s letter “important”.

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“Forcing companies to enable hacking could compromise users’ privacy,” Mr Pichai said in a series of tweets. While Google, like other tech companies, co-operates with law enforcement in criminal investigations, that is “wholly different than requiring companies to enable hacking of customer devices and data”, he said, which “could be a troubling precedent”.

The FBI’s decision to take its row with Silicon Valley over encryption technology to the courts has been brewing for almost two years, after Apple introduced greater security and privacy controls to the iPhone with 2014’s iOS 8 update.

By involving the San Bernardino case, Silicon Valley companies are forced to choose between abandoning their privacy principles and being seen as impeding an investigation into a terrorist attack.

“The PR optics could not possibly be worse for Apple,” wrote tech industry analyst Ben Thompson in a blog post. “It’s a case of domestic terrorism with a clear cut bad guy and a warrant that no one could object to, and Apple is capable of fulfilling the request.”

Dianne Feinstein, the California senator and vice-chair of the senate intelligence committee, said that if Apple did not voluntarily comply with the order, she would put forward legislation to require it, after previous efforts to do so last year failed.

“We have had this terrorist act in my state where 14 people were killed, and there is a phone encrypted that could yield additional information,” Sen Feinstein told CNN. “And I believe that, as a government, we have every responsibility and duty to see that Apple provides that information.”

Speaking at an MSNBC town hall, Republican presidential candidate Donald Trump said: "I think it is disgraceful that Apple is not helping . . . we should force them to do it."

But others in Washington sided with Apple.

Ron Wyden, US senator for Oregon, said the FBI’s request was “bad for Americans’ online safety and security” and could “empower repressive regimes” by giving them a “blueprint” for how to evade encryption.

“This unprecedented reading of a nearly 230-year-old law would create a dangerous precedent that would put at risk the foundations of strong security for our people and privacy in the digital age,” he said in a longer message posted to Twitter. “This move by the FBI could snowball around the world.”

Tech industry groups have also supported Apple.

“If governments compel tech companies to weaken the security that users demand, they are also creating the vulnerabilities that hackers, terrorists or other nefarious actors need,” said Computer & Communications Industry Association president Ed Black.

The Software and Information Industry Association agreed that the order against Apple would do “more harm than good”.

Alex Abdo, staff attorney at the American Civil Liberties Union, said the government request "risks setting a dangerous precedent". "If the FBI can force Apple to hack into its customers' devices, then so too can every repressive regime in the rest of the world," he said.

- Copyright The Financial Times Limited 2016