Beijing, China (CNN) -- The lawyer for an American citizen sentenced to eight years in prison in China is calling his sentencing "harsh."
Xue Feng, a geologist who is a naturalized U.S. citizen, was charged with violating China's state secrets.
"The eight-year prison sentence is harsh," Xue's lawyer Tong Wei told CNN on Tuesday. "The key question in the case is the definition of 'state secrets.'"
During the closed door trial, Xue was said to have argued that the information he gathered is data that the oil sector in other countries would make public.
But China said Xue's actions endangered the country's national security.
The Chinese media has downplayed Xue's case. Except for a few short reports quoting foreign news agencies, the local media did not report on it.
Foreign ministry spokesman Qin Gang disagreed Tuesday that the case may scare foreign firms from doing business in China.
"Do you think we should release him without charge and then others will say China's system is fair and transparent?" he told reporters. "The judicial authorities are the ones to comment on this, but I want to tell you that during the trial, the legal rights of the defendant were fully guaranteed."
On Monday, the U.S. Embassy called for the release of Xue, who in addition to the prison sentence was fined about $29,500 for allegedly providing intelligence abroad.
"I believe the time has come for Dr. Xue, who has already been detained for two and a half years, to be released," said U.S. Ambassador to China Jon Huntsman.
Qin dismissed those calls.
"The Chinese judicial organs are dealing with this case strictly according to Chinese law, and it is China's internal affair, which outsiders shouldn't interfere in," he said. "China's judicial sovereignty brooks no interference."
University of Chicago's Dr. David B. Rowley, Xue's former professor who has rallied for his release, said Xue is languishing in prison on vague charges.
"I find this whole thing just unbelievable in no small part because the rationale is just so thoroughly flawed," Rowley said.
Xue "has always been a straight shooter," Rowley said. "He was not ... a wheeler-dealer type." He is "an honest, hard worker and this came as a real surprise to him as well."
Xue was working in China as a leading geologist for the Colorado-based IHS Consulting firm, a global provider of energy-related information, Rowley said, and the information Xue was privy to did not include state secrets.
While Rowley said he was not privy to the specific database mentioned in Xue's indictment, the professor said the pieces of information commonly contained in such databases are not state secrets.
"These types of databases usually contain information related to the petroleum potential of a given area, and that might include what wells already have been drilled and information on the geology and geophysical or underlying structure of these areas. That's pretty much it," he said.
Xue's job as a leading consultant for IHS involved acquiring and reselling this type of data, Rowley said.
He said that as a petroconsultant, Xue thought he was viewed favorably by the Chinese because he was able to sell to Chinese officials similar data from countries in which the Chinese had drilling interests.
Rowley said Xue had resigned from IHS at the time of his arrest and believed that the warnings issued by Chinese officials concerning the database were not issued against him, but against his employers, he said.
"IHS is extremely disappointed at the news and is very sympathetic to the situation. We are continuing to work with our advisors on the issue," said IHS spokesman Ed Mattix.
CNN Producer Wen-Chun Fan contributed to this report.