The wife of an alleged American spy appealed to Russian President Vladimir Putin on Wednesday to free her husband, who she said was looking frail and unwell in a former KGB Moscow prison.

Cheryl Pope, trembling and struggling with her words, said she met her husband Edmond at Moscow's Lefortovo prison, where he has been held since April for allegedly collecting information about an underwater missile.

"I was able to see him ... and we embraced. The first thing he said to me was 'I'm innocent' and I said 'I know you are'," she told reporters, trying to hold back her tears.

"I would just like to ask Mr. Putin to please look at my husband as an individual and to see there's a mistake being made here."

Russia's FSB domestic counter-intelligence agency, a successor to the Soviet-era KGB, has been quoted as saying that Pope was charged with crimes that could send him to jail for 20 years after he collected information about the missile.

Two Pennsylvania congressmen urged Moscow earlier this month to free the former naval officer, saying he was not a spy but merely a businessman who openly bought technology and sought joint ventures with Russian firms.

A spokeswoman for Congressman John Peterson also called on Putin to review Pope's case, saying Moscow had detained the wrong man.

"This is a case of mistaken identity and we plead with President Putin to please look at this as an individual case. He needs to come home, he needs to be with his family, he's ill, we need him to come home," the woman said, reading a statement from the congressman.

His wife said she knew little about her husband's business in Russia or the charges against him, adding that her brief conversation with him in the waiting room at Lefortovo prison concentrated on family affairs.