The brother of the Paul Whelan, the former US marine arrested in Russia on espionage charges, believes his twin is being used as “a pawn in some larger scheme”, having found himself “in the wrong place at the wrong time”.

David Whelan told the Guardian his family have not been given any details of what his brother is alleged to have done. He said there has been no official confirmation of a Russian press report claiming Paul Whelan was given a USB drive containing the names of people employed at a top secret state organisation.

He also said the Whelan family have not been given any new information about Paul since the US ambassador visited him in Lefortovo prison in Moscow, where he has been held since his arrest on 28 December.

The lawyer assigned to the prisoner does not speak English and Paul Whelan, who runs security for a Michigan auto parts firm and who was in Moscow to attend a wedding, only speaks a few words of Russian, his brother said.

There has been speculation that Whelan was arrested with the intention of exchanging him for Russians in prison in the US, such as Maria Butina, who pleaded guilty last month to conspiracy to infiltrate Republican political circles. She is cooperating with federal prosecutors.

On Saturday, the Russian foreign ministry said a Russian had been detained the day after Whelan’s arrest in the US Pacific territory of the Northern Mariana Islands and transferred to Florida.

The Russian man, Dmitry Makarenko, had been accused in federal court in June 2017 of conspiring to export defence articles, including night-vision scopes, from the US to Russia without approval.

The Russian deputy foreign minister, Sergei Ryabkov, dismissed suggestions that Whelan may be part of a prisoner swap. “I see no reasons to raise this issue in context of exchanges,” Ryabkov said, according to the Interfax news agency. “We should undergo all the procedures needed in this situation.”

David Whelan said no official had mentioned the possibility of an exchange to him. “The family’s focus is getting Paul home and whatever means we can use to do that I would support,” he said in a phone interview from Toronto.

Paul Whelan holds four passports – US, UK, Canadian and Irish – as he was born in Canada to British parents, moved to the US and served in the marines, and has an Irish grandfather. The four governments will coordinate how to handle the case over the next few days, David Whelan said. The US has so far taken the lead as his brother entered Russia on his US passport.

David Whelan welcomed remarks in support of his brother by the British foreign secretary, Jeremy Hunt, on Friday, particularly his warning to Russia not to use its prisoner as a geopolitical pawn.

“I think Paul is perhaps a pawn in some larger scheme,” David Whelan said. “I think he was definitely in the wrong place at the wrong time, and I think the question then becomes whether it is worth trying to dig into what the rationale is for why he was picked up.”

He pointed to the coincidence that a domain name his brother once used, paulnwhelan.com, was purchased in November by an anonymous buyer using a Hong Kong IP address.

“Who would be buying paulnwhelan.com right out of the blue in the middle of November 2018, six weeks before the Russians pick Paul up for spying,” David Whelan said. “So you have so many dots you can’t possibly connect without more details.”

He said he did not know what to make of allegations published in the Russian media outlet, Rosbalt, that his brother had cultivated contacts from the Russian defence and security services for a decade, and had been arrested in his hotel room with a USB drive containing classified information.

“I think it’s difficult to know whether it’s accurate or not,” he said. “I would feel more confident if it had come from the Russian government in an official statement. I don’t understand why, over a week since he was detained, there is no rudimentary information on what happened, why he was picked up, what he was found with. Surely if that was available that would be relatively easy to release.”

He said the family have had no contact with Vladimir Zherebenkov, the lawyer assigned to represent his brother, and is unsure how he came to be hired, as the US embassy only recommends English-speaking lawyers. “It’s our understanding that he doesn’t speak English, which is a little bit of surprise,” he said.

Paul Whelan speaks so little Russian that when US diplomats visited him on Wednesday he did not have his glasses, his brother said. He had not known how to ask for them in Russian and guards were not allowed to talk to him in English.

The family have set up an account which will allow Whelan to buy basics like toilet roll and razors in prison but, because of the Orthodox Christmas holiday, they have not been able to transfer funds.

David Whelan said he had been unaware of his brother’s interest in Russia. “When we meet at my folks’ house or when we email, Russia never comes up, so it’s not like he’s banging on about it all the time,” he said. “I don’t know I would have called him a Russophile.”

Paul Whelan had been in contact with Russians with military backgrounds through the social media website Vkontakte, but his brother said he saw nothing unusual in that.

“Without the context of him sitting in a Russian jail, I’m not sure that it’s really that odd,” he said. “The fact that he is on social media in touch with people with similar backgrounds, I don’t find particularly surprising.”