Jason Hanna and AnneClaire Stapleton, CNN - A US citizen and corporate security director detained in Russia on accusations of spying is a retired Marine who was in Moscow for a wedding, his twin brother said Tuesday.

Paul Whelan, 48, of Novi, Michigan, was arrested Friday in Moscow on suspicion of carrying out an act of espionage, Russia's Federal Security Service (FSB) has said. His family rejects the accusation.

"We are deeply concerned for his safety and well-being. His innocence is undoubted and we trust that his rights will be respected," Whelan's brother, David Whelan, said in a statement released Tuesday to CNN.

Paul Whelan is director of global security for Michigan-based automotive components supplier BorgWarner, where he has worked a few years, the company said Tuesday.

Paul has been to Russia many times for work and personal business, and he flew to Moscow on December 22 to attend a wedding ceremony for a fellow ex-Marine and a Russian woman, David Whelan said.

When Paul didn't arrive at the wedding on Friday, a friend messaged him but received no response, the brother said.

The family learned about Paul's detention only on Monday morning after media reports emerged, David Whelan said.

"Knowing that he's not dead, it weirdly really helps," David Whelan said. "When we couldn't get ahold of him initially, we were worried, and we are still worried now, but at least we know he is alive."

Paul Whelan was born in Canada to British parents, but lives in Michigan now and served multiple tours with the US Marine Corps in Iraq, his brother said. The US State Department has said he is a US citizen.

The family has contacted congressional representatives, the US Embassy, and the State Department for information and assistance, he said.

"I think there's really just one goal, which is ... to get Paul back home."

Charge could bring up to 20 years in prison

The FSB, Russia's domestic intelligence agency, announced Whelan's arrest on Monday.

"The investigation department of the Federal Security Service of Russia initiated a criminal case against a US citizen under article 276 of the Criminal Code of the Russian Federation. The investigation is underway," the statement continued. Article 276 is espionage.

If found guilty, Whelan faces 10 to 20 years imprisonment, Russia's state-run news agency TASS reported. Further details about the reasons for or circumstances of his detention weren't immediately released.

The Russian Ministry of Foreign Affairs "formally notified" the United States of the detention, a US State Department spokesman said Monday.

"Russia's obligations under the Vienna Convention require them to provide consular access. We have requested this access and expect Russian authorities to provide it. Due to privacy considerations, we have no additional information to provide at this time," said a statement from the State Department.

Worked for BorgWarner since 2016

Paul Whelan has worked for BorgWarner since 2016, company spokeswoman Kathy Graham said. She noted BorgWarner has no facilities in Russia.

Graham said she believes Whelan was on a private trip, taken during the company's annual holiday shutdown, when he was arrested.

BorgWarner has contacted the US government to see if the company can be of any assistance, Graham said.

Whelan travels extensively, his brother said.

"My understanding is that he was responsible for looking at the physical security of sites for his employer, to make sure that things couldn't be stolen or be broken into, to remove the opportunities for people to have access to things they shouldn't have access to," David Whelan told CNN's Poppy Harlow in a phone interview.

"But it wasn't cybersecurity. It wasn't body-guard type of security. It was much more about the physical plant."

Previously, Paul Whelan was a senior manager in the global security and investigations group for Kelly Services, according to an interview he gave to Security Magazine in 2013.

Whelan worked for Kelly Services -- a US-based, global office staffing company -- until 2016, company spokeswoman Jane Stehney said.

The 2013 Security Magazine article said Whelan's job at Kelly Services involved preventing workplace violence.

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