Retired US Marine Paul Whelan was detained by Vladimir Putin's secret services because he received an electronic database with a list of 'secret' employees of a Russian agency, it was reported in Moscow.

The 48-year-old had fallen under suspicion on frequent visits to Russia because while saying he went to have 'fun' he shunned 'pretty women' and instead made contacts with males who might have access to confidential information.

Minutes after receiving a flash drive in his five-star hotel room in Moscow, armed Federal Security Service (FSB) operatives moved in and detained him, reported Rosbalt news service, which has close links to the security services.

'The American received an electronic carrier in the room with a list of all employees of one of the secret Russian departments,' said the first of several reports.

'Five minutes after the transfer, FSB officers broke into the room and detained a suspect of espionage.

'On examination, they found a flash card with secret information.'

Russian media claimed retired US Marine Paul Whelan (pictured) was in possession of 'secret information'

Whelan, a resident of Michigan, was arrested on December 28 at the Metropol Hotel in Moscow (pictured)

Minutes after receiving a flash drive in his five-star hotel room in Moscow, armed Federal Security Service (FSB) operatives moved in and detained him, it is claimed. One of the rooms at the hotel is pictured

Rosbalt stated that Whelan, a corporate security executive, was 'caught red-handed immediately after receiving a media with information containing state secrets.

'It was about a list of persons that is not subject to disclosure and has long been the object of keen interest of US intelligence.

'As a source in the special services of the Russian Federation told Rosbalt, the operation to detain Paul Whelan took place in his room at the Metropol Hotel.'

Whelen - whose family insist he is innocent - had been engaged in secret activities for a decade, according to an intelligence source cited by Rosbalt.

'Whelan for 10 years led intelligence activities, and he found 'objects' (sources) to get the necessary information on the Internet,' reported the news outlet.

In a follow-up report, Rosbalt claimed Whelan 'used quite unusual methods in his spying activities'.

The source said that about ten years ago he started registering on the various internet websites and forums attended by large numbers of Russians.

'The American man posted about his love to Russia, his wish to master the Russian language, to visit Moscow,' stated the report.

Some of those Whelan befriended online were of interest to US secret services, it was claimed, and these people 'might have access to secret information'.

The report went on: 'Having established solid contacts with Russians online, Whelan began to visit Moscow in person.

'He pretended he had come to Moscow "to have fun" and he always met his internet friends.

'It was noticeable that Whelan was not at all interested in pretty Russian women but preferred to drink with his male friends.'

In these sessions 'the US citizen tried to understand if they possessed information interesting for US secret services, or if somebody from his close circle might have such access', it is claimed in the report.

If the person looked potentially interesting, Whelan 'aimed to establish maximum trusting relations with them, (and) even attended family parties.

'At the same time the foreigner "worked" with them in order to receive the required information.'

No names were given of people Whelan had allegedly targeted. Nor was any proof given to support the allegations in the Rosbalt reports.

Meanwhile, the Nezygar Telegram channel - seen as having insider information in Moscow - cited a source saying Whelan 'was involved in spying activities since his work in recruiting company Kelly Services that has an office in Moscow'.

The report predicted that law enforcement 'will have to go through the whole database of those recruited by Kelly' over a ten-year period.

Whelan posted these photos in September showing himself on a Bombardier challenger jet

Paul Whelan is seen in a 2006 photo taken outside the Kremlin in Moscow. He visited Russia regularly, and his brother says he was there for a wedding when he was arrested

An archived version of paulnwhelan.com (above) was reviewed by DailyMail.com and describes a 2006 trip to Russia. The site has since been removed from the Internet Archive

It would be necessary 'to check if anybody had been recruited' as a result of Whelan's activities.

'This American company was dealing with recruiting people for top jobs in strategically important Russian companies in Moscow,' stated Nezygar.

Its recruitment was in potentially sensitive sectors such as IT, telecommunications and pharmaceuticals, as well as sales and marketing.

Rosbalt reported that Whelan's lawyer Vladimir Zherebenkov refused to comment on the case.

He said he was under a legal ban preventing him sharing information.

But he said that his client Wheelan 'looks confident, possessed a great sense of humor and hopes that the investigation is not biased', according to Rosbalt.

'We will complain in the Moscow city court on the fact of his arrest,' he was quoted as saying, indicating he was seeking non-custodial detention for the American while the investigation goes on.

'There was no evidence presented that Whelan can hide or put somebody under pressure.

'The defense supposes that Whelan deserves other limitations other than arrest.'

Whelan, a resident of Michigan, was arrested on December 28 at the Metropol Hotel in Moscow and is now being detained in the city.

U.S. ambassador to Russia Jon Huntsman met with Whelan in Moscow on Wednesday as the American government seeks answers about his arrest.

Huntsman said he offered support and assistance to Paul Whelan, and later spoke to the man's family by phone, but he would not discuss the case in detail.

The ambassador said the U.S. complained to the Russian government about the length of time it took them to grant consular access to Whelan, who was arrested Friday.

Whelan is seen on a prior trip to Russia. He visited regularly for work and pleasure

Whelan was in Moscow to attend a wedding when he disappeared, his brother, David Whelan, said Tuesday. He arrived December 22 and was scheduled to stay through Sunday.

Whelan's family, in a statement that David posted on Twitter, said: '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.

The Marine Corps on Wednesday released details of Whelan's service record. He served in the Marine Corps Reserves from 1994 to 2008 and was convicted of larceny in a special court-martial in January 2008.

The Marine Corps did not immediately provide details of the court-martial conviction beyond saying it was based on 'several charges related to larceny.'

Whelan attained the rank of staff sergeant in December 2004 after the first of two deployments in Iraq. He was an administrative clerk and administrative chief.

He was given a bad-conduct discharge in December 2008 at the rank of private. His last place of duty was at Marine Corps Air Station Miramar in California.

David said in an interview that his brother had been to Russia several times previously, so when a fellow former Marine was planning a wedding in Moscow, he was asked to go along to help out.

David said that it was while searching the internet Monday that he learned of his brother's arrest.

'I was looking for any stories about dead Americans in Moscow, so in a way it was better than finding out that he had died,' he said.

David said he has no idea why his brother was targeted by the Russian security services. Paul Whelan had traveled to Russia in the past for work and to visit friends he had met on social networks, his brother said.

'I don't think there's any chance that he's a spy,' David told CNN.

Paul Whelan lives in Novi, Michigan, and is director of global security for BorgWarner, where he has worked since early 2017.

'He is responsible for overseeing security at our facilities in Auburn Hills, Michigan, and at other company locations around the world,' company spokeswoman Kathy Graham said in a statement.

She said BorgWarner does not have any facilities in Russia.

Paul Whelan previously worked for Kelly Services, which does maintain offices in Russia, his brother said.

Whelan's defunct website reveals his enthusiasm for the country and multiple trips there.

His website, paulnwhelan.com, describes a 2006 visit to Russia, which appears to be his first trip to the country. An archived version of the site, which is no longer available, was reviewed by DailyMail.com.

'My recent visit to Russia was a great experience. I had quite an enjoyable time exploring Moscow and Saint Petersburg,' he wrote.

Whelan (above) served multiple tours of duty in Iraq as a Marine

Paul Whelan is seen in a family photo provided by his brother. The Marine veteran was arrested in Russia on December 28 on espionage allegations

'Having grown up during the Cold War, it was a dream of mine to visit Russia and meet some of the sneaky Russians who had kept the western world at bay for so long!!'

'I was fortunate enough to meet nice people and had several pleasant excurisons throughout the country. My language skills are certainly improving!!'

The website describes a 'friend' named Maxim that Whelan made on his travels, who was 'currently serving with the Russian Army in Moscow' at the time.

'We met in Moscow and visited many interesting areas of the city together. We have stayed in touch with one another and have shared many interesting stories and experiences,' Whelan wrote.

'The Russian people were very polite and kind to a stranger who didn't speak the language and spent a lot of time wandering around the Metro without a clue as to where he was going!!'

'The Russian language is very difficult to learn, but I've been slowly studying and learning from my friends,' he continued.

The website's photos have not been preserved, though the captions remain.

In one, Whelan ironically notes: 'This is 'Lubyanka' where the KGB has our spies locked in the basement!!'

Lubyanka is the popular name for the headquarters of the FSB, the same agency that arrested Whelan on December 28. It is the successor agency to the Soviet Union's KGB.

Currently, Whelan has an account on Russian social media site VK, where he has 70 friends and regularly posts updates in rudimentary Russian, including one that said 'President Trump Forward!!'

Experts on the Kremlin quickly speculated that the arrest was bogus, and an attempt to create leverage against America in the case of Russian woman Maria Butina (above)

He also posted a photo of himself on the site wearing a Spartak Moscow football jersey.

Experts on the Kremlin have speculated that Paul Whelan's arrest was bogus, and an attempt to create leverage against America in the case of Maria Butina, a Russian woman who recently pleaded guilty in the U.S. to acting as an illegal foreign agent.

At a press conference last week, Vladimir Putin denied that Butina was a Russian agent, saying that the 'law of retaliation states, 'An eye for an eye or a tooth for a tooth,' but insisting 'we will not arrest innocent people simply to exchange them for someone else later on.'