The Russian lawyer for a Michigan man jailed on espionage charges in Moscow says his client's detention is "baseless." Paul Whelan, a former U.S. Marine, was arrested in Russia a week ago and accused of spying. He was formally charged with espionage on Thursday.

CBS News correspondent Jan Crawford reports that U.S. intelligence and State Department sources have told CBS News they are confident Whelan is not a spy. His family also denies all the accusations against him.

Whelan's Russian attorney has said that his client is expected to be in a Russian prison until the end of February, but he is hoping Whelan will be granted bail.

It emerged on Friday that Whelan holds dual United Kingdom citizenship, drawing another party into the international standoff. Ireland's national broadcaster RTE reported Friday that Whelan, who was born in Canada, also holds Irish citizenship.

U.S. officials have not confirmed that Whelan is a citizen of any other country, but a senior U.K. official did confirm it was looking into the case.

The British government warned Russia not to try to use Whelan as leverage, with Foreign Secretary Jeremy Hunt telling BBC News on Friday that London, does not "agree with individuals being used in diplomatic chess games... We are all extremely worried about him and his family."

"We need to see what these charges are against him," Hunt said. The top diplomat said the U.K. had offered to send consular officials to visit Whelan but that Tehran had not allowed a visit as of Friday.

Whelan's family says he was in Russia for the wedding of a friend. They believe he has been unwittingly been caught up in the spy game and that Russia is using him as a pawn to try and get back one of its spies, Maria Butina, who is in a U.S. prison on charges of espionage.

The 48-year-old retired Marine, who's been jailed for a week in solitary confinement, has reportedly asked for an English-speaking cellmate and requested toothpaste, a brush and clothing.

Whelan reportedly doesn't speak Russian well and has been using a translator.

CBS News national security contributor Mike Morrell -- the former deputy director of the CIA, has said Whelan's arrest should be a warning to any American thinking about going to Moscow, that now is not a good time to visit Russia.