Feng's case has highlighted the risks of doing business in China for those holding foreign nationalities [GALLO/GETTY]

A court in Beijing has upheld the conviction of an American geologist on the charge of betraying state secrets.

Xue Feng was arrested in November 2007, and tried to appeal against a conviction that resulted in an eight-year prison sentence handed down in July last year.

Jon Huntsman, the US ambassador, attended the hearing on Friday, and urged the Chinese government to release Xue.

"We ask the Chinese government to consider an immediate humanitarian  release of Xue Feng," he said.

"I am extremely disappointed in the outcome when you consider that the charges are very questionable."

Xue, a Chinese-born US citizen working for a private firm, was first detained over the sale of a database on China's oil industry.

US concerns

At the time of Xue's arrest, he was working for IHS Inc., a US energy and engineering consulting firm . Both Xue and IHS have said they believed the database to be a commercially available product.

According to the Dui Hua Foundation, a rights group, it was only classified as a state secret after Xue had  bought it.

The US has repeatedly raised concerns over whether Xue's rights were being  protected and whether he had access to a fair trial.

The embassy previously said that the case was not handled with the "transparency that would befit a nation which tells us that the rule of law is paramount in all judicial processes".

Barack Obama, the US president, has personally raised Xue's case with  Hu Jintao, his Chinese counterpart.

Xue's arrest and other cases have cast a spotlight on the dangers of doing business in China, especially for those born in China but who have been educated abroad and taken a foreign nationality.