WASHINGTON (AP) — Secretary of State Mike Pompeo said on Wednesday that the U.S. hopes to gain access soon to a former Marine who was arrested in Russia on espionage charges and that “if the detention is not appropriate we will demand his immediate return.”

Paul Whelan, who is head of global security for a Michigan-based auto parts supplier, was arrested on Friday. In announcing the arrest three days later, the Russian Federal Security Service said he was caught “during an espionage operation,” but it gave no details.

Whelan, 48, was in Moscow to attend a wedding when he suddenly disappeared, his brother David Whelan said Tuesday.

Pompeo, speaking in Brazil, said the U.S. is “hopeful within the next hours we’ll get consular access to see him and get a chance to learn more.”

The U.S. has “made clear to the Russians our expectation that we will learn more about the charges and come to understand what it is he’s been accused of and if the detention is not appropriate we will demand his immediate return,” Pompeo said.

Whelan’s family said in a statement David Whelan posted on Twitter, “We are deeply concerned for his safety and well-being. His innocence is undoubted and we trust that his rights will be respected.”

The Russian spying charges carry a prison sentence of up to 20 years.