Mark Zuckerberg launched an implicit attack on Donald Trump, sharply criticising the Republican presidential frontrunner’s rhetoric on immigration and trade by citing “fearful voices calling for building walls.”

In his keynote address to his company’s annual Facebook F8 developer conference in San Francisco, the Facebook founder appeared to compare Trump’s candidacy to oppressive regimes who limit free speech by blocking access to the Internet.

Zuckerberg said he was “starting to see people and nations turning inward, against this idea of a connected world and a global community. 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.”

The Facebook CEO said the social network’s mission was to “connect the world” with projects including Aquila, a high-altitude aircraft that can fly unmanned for months at a time, beaming Internet access to isolated regions in the developing world. “We’ve gone from a world of isolated communities to one global community and we are all better off for it,” Zuckerberg said.

“Our lives are connected,” he went on. “Whether we’re welcoming refugees fleeing wars or an immigrant seeking a new opportunity, whether we’re coming together to fight global disease like Ebola or to address climate change, I hope that we have the courage to see that the path forward is to bring people together, not push people apart, to connect more, not less.”