The former US marine detained in Moscow has been charged with spying and faces 20 years if convicted, according to the Interfax news agency.

Paul Whelan, who is head of global security for a Michigan-based car parts supplier, is being held in the Lefortovo detention facility, a former KGB prison in the Russian capital.

Whelan’s lawyer, Vladimir Zherebenkov, declined to comment on the charges but said that under the terms of the arrest order, Whelan was expected to remain in custody in Moscow until at least 28 February.

“I consider his detention and arrest baseless. It’s based on investigators’ supposition that he will hinder the investigation process. We are asking for bail instead,” Zherebenkov told Reuters.

On Thursday, a Russian news outlet claimed Whelan was arrested just minutes after receiving a USB drive that contained the names of people employed at a top secret state organisation.

Citing a security service source, Rosbalt news agency said the 48-year-old American received the USB drive from a Russian citizen who visited him in his room at the Metropol hotel in Moscow on Friday. Officers from the FSB intelligence agency then reportedly burst into the room and arrested Whelan. The information could not be independently verified by the Guardian. Rosbalt did not say what had happened to the Russian citizen.

The news agency said that according to its source Whelan began making contact with potential Russian informants on internet forums and chatrooms about 10 years ago. He would then, the source said, meet up with his online acquaintances individually in Moscow “over a bottle”.

“The US citizen tried to determine if his acquaintance possessed information that could be of interest to American intelligence services, or if anyone in his close circles had access to such information,” read the Rosbalt report. The news agency often cites unnamed security service sources in its articles.

Whelan’s brother, David, told the Guardian: “We have not had any details from the state department about the circumstances of Paul’s arrest.”

A social media page apparently belonging to Paul Whelan on VK, or VKontakte, the Russian version of Facebook, contains at least one clear reference to a visit to Moscow, as well as a number of short Russian-language messages such as “Happy Victory Day” and “Forward, President Trump”. In one photograph, he is wearing a Spartak Moscow football top. The pinned message at the top of his VK page reads: “Next stop, Moscow … ”

Whelan has 59 friends on his VK page, including some former students at the Military University of the Ministry of Defence of the Russian Federation in Moscow.

One of his VK “friends” said he had first been in touch with Whelan more than a decade ago, when the two exchanged contacts on a now defunct pen pals website.

“When he visited Russia in 2008, I met him in person, we had a brief sightseeing tour of my city. I haven’t seen him since then,” the VK friend said, speaking on condition of anonymity. “This time I was not aware that he was in Russia until I sent him my Christmas greetings on the 25th, and he responded saying that he’s in Moscow, and that he plans to go to St Petersburg next.”

Zherebenkov said his client was holding up well and had a good sense of humour.

The US ambassador to Russia, Jon Huntsman, visited Whelan in prison on Wednesday, a move described as “a rookie mistake” by one Russian foreign policy analyst.

“He should have sent a career consular officer,” said Vladimir Frolov. “An ambassadorial visit by a political appointee escalates the situation and raises the stakes, makes it harder to resolve the situation.”

Huntsman has been US ambassador to Russia since October 2017.

A state department spokesperson said: “Ambassador Huntsman expressed his support for Mr Whelan and offered the embassy’s assistance. Ambassador Huntsman subsequently spoke by telephone with Mr Whelan’s family. Due to privacy considerations for Mr Whelan and his family, we have nothing further at this time.”