Dickens wrote:
No, he'd maintain his citizenship, but he would be subject to prosecution. Do you doubt it? Read anything about Bobby Fisher, (sp?) the chess player who has been wanted by American authorities for the last twenty or so years for the high crime of playing chess in some communist country where Americans were then prohibitted from carrying on business.
Fischer played in a match in 1992 in Yugoslavia, which was subject to sanctions because of the civil war then in progress. Fischer ignored the sanctions, tearing up a letter from the State Department on camera. He hasn't been able to return to the United States since then, though the government didn't really try to prosecute him until they sought his extradition from Japan last year. But he was then offered Icelandic citizenship and has, apparently, been living in Iceland since then.