Tension is mounting between the Donald Trump campaign and Facebook CEO Mark Zuckerberg after the two billionaires took swipes at each other following Facebook’s F8 developer conference on Tuesday.

“I hear fearful voices calling for building walls and distancing people they label as others,” Zuckerberg told an audience of 2,000 people at the conference in San Fransisco. “If the world starts to turn inwards, then our community will just have to work even harder to bring people together.”

He later posted on Facebook that his latest speech was “personally important” to him and “different from any other speech I’ve given.”

He also said that his message was not just for America, but to help connect people around the world. “It’s about having the courage to choose hope over fear,” he wrote.

The Trump campaign was quick to respond. “I’ll take Mark Zuckerberg seriously when he gives up all of his private security — move out of his posh neighborhood and come live in a modest neighborhood near a border town,” Katrina Pierson, a spokeswoman for the Trump campaign, told CNBC. “Then I’m sure his attitude would change.”

The exchange comes as Zuckerberg attempts to play a more hands-on role in global politics. His company, Facebook, has come under criticism for censoring “hate speech” in Germany in reference to the influx of over 1 million migrants into the country.

He has also met with world leaders over the years including President Barack Obama, Indian Prime Minister Narendra Modi, and Chinese President Xi Jinping, despite Facebook being banned in China.

He has also spoken out on the issue of terrorism, recently saying that “love” will defeat the Islamic State.

Trump, meanwhile, has a Facebook following of nearly 7 million people.

Both the Trump campaign and Zuckerberg have confirmed they will not be commenting further on the matter.

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