Facebook CEO Mark Zuckerberg takes to the stage on Monday at the world's biggest mobile fair in Barcelona just as US tech giants clash with authorities in the latest debate pitting privacy against security.

The controversy emerged earlier this month when Apple refused to help the FBI break into an iPhone belonging to the late Syed Farook, who along with his wife went on a deadly shooting rampage in California's San Bernardino in December.

Apple claims that cooperating with the probe would undermine security for its devices, while the US government counters it is a one-time request that will aid an important investigation.

Zuckerberg, who will give a keynote speech at the Mobile World Congress, has been at pains to plug privacy features on Facebook in recent years.

The 31-year-old has not yet spoken publicly about the spat but last week Facebook issued a statement in support of Apple.

The social media giant said that while it condemned extremism it would "continue to fight aggressively against requirements for companies to weaken the security of their systems."

"These demands would create a chilling precedent and obstruct companies' efforts to secure their products," it added.

Apple has vowed to fight a judge's order that it should create an operating system that would allow the FBI to brute force its way into the iPhone.

Just like Facebook, Apple CEO Tim Cook warned last week that complying with the order would set a dangerous precedent and open the door for governments and even criminals to access sensitive data in the future.

Facebook and privacy  

Apple's dispute with the US government is just the latest clash between a tech firm and authorities, and many of the sector's biggest names have sided with the iPhone maker.

Richard Yu, consumer devices chief for Chinese electronics giant Huawei, said on Sunday in Barcelona that privacy was "the most important thing to the consumer."

"We should really protect the consumer's privacy and security. Personally, I support Apple's, Tim Cook's idea," Bloomberg quoted him as saying on the sidelines of the presentation of Huawei's first laptop.

Zuckerberg's address in Barcelona will also be watched closely for any comment on concerns in Europe over how the world's largest social network handles personal data.

Facebook was long accused of brushing aside users' privacy concerns, and while Zuckerberg has strived to win back trust with a flurry of features, the social network is still in the eye of the storm.

Earlier this month, it was given three months by France's CNIL privacy watchdog to stop storing data on people who do not have an account with the social network.

The decision comes after Facebook lost a similar fight with Belgium's privacy watchdog in November when a court ordered it to stop storing personal data from non-users.

On a regional level, the European Union's 28 privacy watchdogs have been coordinating probes into possible violations of EU law by Facebook's policy for handling personal photos and data.

Ahead of the speech, though, Zuckerberg appeared relaxed, posting photos of himself jogging in Barcelona on his Facebook page.

He also made a surprise appearance at Samsung's press conference late on Sunday to unveil its new flagship smartphones.