The US charge d'affaires in Abu Dhabi urged the United Arab Emirates on Friday to free American Zack Shahin, who is in jail on fraud charges and has been on a hunger strike since May 14.
The embassy said L. Victor Hurtado visited Shahin at the Dubai Central Jail on Tuesday and that "after more than six weeks, obviously there are serious concerns about Mr Shahin's health.
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Shahin, at the time managing director of property developer Deyaar Development, was arrested in 2008 and charged the following year with embezzling more than 98 million dirhams (then $27 million).
He was also charged with taking bribes.
However, he has never been convicted of the alleged offences.
The embassy said there are "significant concerns" over the case, including Shahin's detention for more than a year without charge, failure to release him on approved bail requests and his apparent unequal treatment compared with others accused of financial crimes in the United Arab Emirates.