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U.S. Ambassador to Russia Jon Huntsman visited on Wednesday with Paul Whelan, the American businessman detained in Russia, a State Department spokesperson said.

"Ambassador Huntsman expressed his support for Mr. Whelan and offered the Embassy’s assistance," the spokesperson said, adding that Huntsman also spoke with Whelan's family.

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The security executive and retired Marine was arrested on Monday by Russian officials who charged him with spying.

The Russian Federal Security Service said its investigation into Whelan was ongoing, adding that he could face up to 20 years in prison if convicted.

Whelan's twin brother, Dave, said he was “100 percent confident” that his brother is not a spy.

“Russia was just one of the many places he enjoyed going to. He had social media friends that he picked up over the years. They’re in Russia, and so going to Russia would be a normal thing,” the brother told NBC News' Hallie Jackson.

Paul Whelan had visited Russia multiple times in the past, and was attending a friend’s wedding in Moscow when he was detained, his brother said.

Secretary of State Mike Pompeo said the Trump administration would demand Paul Whelan’s release if the charges against him were unfounded.

When asked if the administration had contacted Whelan’s family, David said he doesn’t believe “anybody in my family has spoken to either the secretary or President Trump."