By Stefan J. Bos
Britain's foreign secretary, Jeremy Hunt, accused Russia in a statement of using British citizens as what he called "pawns in diplomatic chess."
He said he was "extremely worried" about former US Marine, Paul Whelan, who has been detained on suspicion of spying. Hunt added that "every support" is being given to the 48-year-old.
In separate remarks, Russia's Foreign Ministry confirmed that Whelan had British citizenship and that in its words The British side has sent "a request for a consular visit" and "work on it is in progress."
His British citizenship was reported by a day to British officials a day after U.S. Ambassador Jon Huntsman Jr. met with Whelan at Lefortovo Prison.
Whelan was born in Canada to British parents and moved to the US as a child. He now lives in Michigan and is director of global security for automotive components supplier BorgWarner.
Whelan traveled to Russia on December 22 and planned to fly home on January 6. Those plans were interrupted when he was suddenly detained in Moscow on December 28.
David Whelan has commented on his brother's arrest. He said his brother had been visiting Russia for business and pleasure for more than a decade and suggested that he had not been involved in illegal spying activities.
"His all career has been around law and order and risk management. And so when you travel into countries, and we know that certain countries in the world can be more dangerous or not and then certain parts of those countries can be dangerous," he said.
David Welan added: "He is the sort of person that you would expect to go into those countries and know where to go and where not to go and also to be able to handle themselves if they found themselves in a difficult situation. So, it is very hard for me to understand how anyone would consider Paul to be someone who would be a lawbreaker."
If found guilty of espionage, Paul Whelan could face up to 20 years imprisonment.
His brother told reporters however that he may be exchanged with Maria Butina, a Russian gun rights activist who was jailed in the United States last month.
The stand-off comes at a time of growing tensions between Russia and the United States over for instance conflicts in Ukraine and Syria and alleged Russian meddling in US elections.
They also have traded spying allegations at regular intervals since the Cold War.