American Paul Whelan, arrested in Moscow and accused of espionage, has in addition to his American passport one from Britain, Canada and Ireland, Whelan’s brother said Friday.

“As for his international connections, our family spans continents, and Paul’s four passports reflect his birth (Canada), parents (Britain), grandparents (Ireland) and choice (United States),” David Whelan wrote in an Op-Ed in The Washington Post.

In the Op-Ed Whelan called on President Donald Trump and lawmakers to “pressure Russia for [Paul Whelan’s] immediate release.”

“Paul is a kind and considerate brother, son and uncle, and a generous and loyal friend. He travels as often as he can, both for work and pleasure. He is many things to many people, but he is not a spy,” David Whelan wrote.

The revelation of Whelan’s passports issued by multiple Western nations further complicates an already complex situation for the 48-year-old. Whelan was arrested by Russian security services on Dec. 28, according to a Dec. 31 statement from the FSB, successor to the KGB. The FSB said Whelan was caught engaging in espionage activity, and unverified Russian news reports further alleged he had for years been involved in spying and was arrested in his hotel room in Moscow with a secret list of Russian government personnel.

Whelan’s family maintains his innocence and said he was only in Moscow for a wedding. A Russian attorney currently representing him also denied the allegations.

Former intelligence officials told ABC News they view the Russian claims with deep skepticism and said Russia might have detained Whelan in an act of “reciprocity” for the arrest of Russian agent Maria Butina in the U.S. One former senior CIA official, Steven Hall, said the fact that Whelan may hold multiple passports doesn’t suggest anything nefarious and said many people have multiple passports for perfectly legitimate reasons.

(MORE: Swap or not, Russia seeks ‘reciprocity’ with ‘spy’ arrest, ex-officials say)

Whelan is employed as head of security at the international auto parts firm BorgWarner based in Michigan, a spokesperson for the company said. Military records show he served as a Marine from 1994 to 2008 when he received a bad conduct discharge for attempted larceny and other charges. Whelan was found guilty of stealing more than $10,000 while deployed to Al Asad Base in Iraq and, around the same time, bounced nearly $6,000 worth of checks, according to military records.

British Foreign Secretary Jeremy Hunt told Sky News Friday that Britain is “giving [Whelan] every support we can, but we don’t agree with individuals being used in diplomatic chess games.”

“Because it is desperately worrying, not just for the individual but their families, and we are extremely worried about him and his family as we hear this news,” he said.

A British official told ABC News the U.S. Embassy in Moscow alerted the British Embassy Thursday that Whelan had a British passport.

The Canadian foreign ministry said today that consular assistance is being provided by their nation as well, “and we are in contact with local authorities to gather further information.”

Whelan was visited in detention in Moscow Wednesday by U.S. Ambassador Jon Huntsman. Thursday, Secretary of State Mike Pompeo told Newsmax the Trump administration is "doing everything we can to make sure [Whelan is] treated appropriately and that we get the information we need."

The CIA and the White House have declined to comment on the case.

“We urge President Trump to intercede on Paul’s behalf,” David Whelan wrote. “U.S. government action will reinforce that Americans traveling abroad should not do so in fear, and ensure other American families are less likely to have their loved ones go missing.”

ABC News’ Elizabeth Mclaughlin and Conor Finnegan contributed to this report.