Paul Whelan was visiting Moscow last week when he was arrested (Picture: PA).
Jeremy Hunt has warned Russia not to use UK citizens as pawns in "diplomatic chess games" after a former US Marine was arrested on spying charges.
The Foreign Secretary said Paul Whelan, a 48-year-old who lives in Michigan in the US, was being given "every support that we can" after it emerged that he also has British nationality.
Paul Whelan, who is head of global security for a Michigan-based car parts supplier, was arrested on Friday.
In announcing the arrest three days later, the Russian Federal Security Service said Mr Whelan was caught "during an espionage operation" but gave no details.
Speaking during a visit to Singapore, Mr Hunt told Sky News that "individuals should not be used as pawns of diplomatic leverage".
"We are giving him every support that 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."
On Wednesday, the Russian government said it had allowed Mr Whelan to have access to US officials seeking answers about his arrest.