Facebook's Mark Zuckerberg criticized the "fearful voices calling for building walls" during his opening remarks at the company's developer conference Tuesday in San Francisco.

The social media company's founder and chief executive said the world has become a global community and warned against people and nations trying to isolate themselves — a possible allusion to GOP presidential front-runner Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE, who has heavily pushed a plan to finish building a wall along the Mexican border to limit the influx of immigrants coming to the country illegally.

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"We've gone from a world of isolated communities to one global community, and we are all better off for it," Zuckerberg said. "But now, as I look around and I travel around the world, I'm starting to see people and nations turning inward — against this idea of a connected world and community."

He added: "I hear fearful voices calling for building walls and distancing people they label as others, for blocking free expression, for slowing immigration, reducing trade and, in some cases around the world, even cutting access to the internet."

Adopting the rhetoric of a politician, Zuckerberg said, "It takes courage to choose hope over fear" and said the company would continue to focus on connecting people.

He did not mention any politician or nation explicitly. But during the speech, he briefly highlighted a number of policy issues including immigration reform, the Syrian refugee crisis, climate change and Ebola.

Zuckerberg has been a vocal advocate for immigration reform, including expanding a visa program for high-skilled immigrants. The Facebook founder's name has even been invoked on the GOP debate stage as candidates argued over the issue.

Zuckerberg made his remarks during the opening of the company's annual developers conference. He described Facebook's 10-year plan, which includes connecting millions of people around the world with basic internet service, as well as making improvements to virtual reality and artificial intelligence technology.