Google chief Sundar Pichai on Wednesday expressed his support for Apple in its standoff with the FBI over unlocking an iPhone as part of a terror probe, warning that creating so-called "backdoors" into encrypted communications could have "bad consequences".

"We want to take a very strong stance against any form of backdoor whatsoever," chief executive Pichai said during a conference at Paris's Sciences Po university, as he waded into the controversy.

"When you create backdooors it leads to very, very bad consequences which always ends up harming users."

Apple has found itself at the heart of a closely watched legal battle after a US judge ordered the tech giant to find a way to unlock the encrypted iPhone of US citizen Syed Farook, a gunman in last year's deadly San Bernardino shootings.

"User privacy is at the heart of what we do," Pichai added, though he noted the company had in the past cooperated with authorities when due legal processes had been followed.

His remarks echoed those made in a series of tweets last week, in which he wrote that giving "law enforcement access to data based on valid legal orders" was "wholly different than requiring companies to enable hacking of customer devices & data".

Apple has won the backing of a number of Silicon Valley firms in its legal fight, with Facebook's Mark Zuckerberg saying Monday that he was "pretty sympathetic" with Apple's quandary.