(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 former Marine and a Russian woman, David Whelan said.

Paul was with the bride and groom at the Kremlin on Friday, acting as a tour guide for wedding guests, his brother said. When Paul didn't arrive at the wedding later that day, the couple filed a missing-person report with Russian authorities, David Whelan said.

The family learned about Paul's detention 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 a hold 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. He served multiple tours with the US Marine Corps in Iraq, his brother said. The US State Department has said he is a US citizen.

Whelan's has contacted congressional representatives, the US Embassy, and the State Department for information and assistance, his brother said.

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

American appears on Russian social media

It appears that Paul Whelan had been using a Russian social media platform similar to Facebook for the past 13 years.

Photos showing Whelan have been uploaded to the VKontakte (VK) social network from around the world for years, according to a profile under his name.

The last status update on the page reads "next stop, Moscow..."

Whelan appears to have posted several comments in Russian last year, including one congratulating the Russian people for "Victory Day," the day of Nazi surrender in 1945, and another one wishing a Merry Christmas.

The page shows that someone last logged into the profile under Whelan's name on December 28, the same day Russian officials said he was arrested in Moscow.

When asked about the VKontakte page, Whelan's brother, David Whelan, said he couldn't confirm whether it belongs to his brother.

"I'm not on Vkontakte so I'm not sure if it's his account. I believe he does have an account. I do not believe he speaks Russian, other than enough words to get around town," he said.

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.

Arrest comes weeks after Russian Maria Butina's guilty plea

Whelan's arrest came 15 days after alleged Russian spy Maria Butina pleaded guilty in US federal court , as part of a deal with prosecutors, to trying to infiltrate Republican political circles and influence US relations with Russia before and after the 2016 presidential election.

Until the plea deal, Butina maintained she was innocent and insisted she was a foreign student interested in bettering relations between the US and Russia. Russian Foreign Ministry spokeswoman Maria Zakharova has said the Russian government views her as a "political prisoner" who did nothing wrong and had been targeted for political motivations.

CNN asked Samantha Vinograd, who served on President Barack Obama's National Security Council from 2009 to 2011, whether Whelan's arrest is a Russian government response to Butina's legal problems in the US.

"(Russian President Vladimir) Putin certainly likes to take what he calls reciprocal measures, and in this case, ostensibly he would want to have some kind of bargaining chip if he chooses to try to negotiate for Maria Butina's release," Vinograd, a CNN national security analyst, told CNN's Brianna Keilar.

While the move might be retaliatory, the cases aren't equal, Vinograd said.

"Maria Butina is in the United States (court system) after an independent law enforcement process was undertaken. She'll get a fair trial. She has access to lawyers and she will not be manipulated by a system that's controlled by an autocratic leader," she said.

"Paul Whelan is not going to have the same benefit while he's in Russia. Vladimir Putin controls law enforcement in Russia. He controls the courts, and he controls propaganda. And thereby, we have to be very clear here that Paul Whelan may be brought before the courts on trumped-up charges with completely fabricated evidence and with a verdict already predetermined," she said.

Traveled to Russia as a Marine; worked for BorgWarner since 2017

Few details about Whelan's previous travels to Russia and his military record were immediately available. But during one of his military tours in 2006, he used his two weeks' leave to visit the country.

2007 online Marine Corps article says he spent the leave "experiencing the post-Soviet era of Moscow and St. Petersburg." An attached photo shows him standing across the Moscow River from the Kremlin. At the time of publication, he was a staff sergeant assigned to the 3rd Marine Aircraft Wing.

Paul Whelan spent two weeks' military leave in Russia in 2006, according to an article posted on the US Marine Corps website. This photo accompanying the article shows Whelan in front of the Kremlin during that trip.

Whelan has worked for BorgWarner since 2017, 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."

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

This story has been updated to reflect that BorgWarner amended the year in which Paul Whelan started to work at the company.