China said Wednesday it was "severely concerned" over the arrest of one of its citizens in the US, one of six Chinese nationals charged with economic espionage.
US prosecutors accused the Chinese suspects, who include three university professors, with a years-long scheme to steal mobile phone technology trade secrets for Beijing's benefit.
"China is severely concerned about this," foreign ministry spokesperson Hong Lei told a regular briefing, adding Beijing would defend its citizens' rights.
According to a 32-count criminal indictment the group led a long-running effort to obtain US trade secrets for universities and companies controlled by the Chinese government.
Among those charged were Tianjin University professor Hao Zhang, who was arrested as he entered the US on Saturday, US officials said.
The five others named in the indictment were believed to be in China, according to a US justice department official.
All could face lengthy prison sentences if convicted. The charges they face include economic espionage, theft of trade secrets and various conspiracy counts, with penalties that could include 10 to 15 years in prison plus fines.
It is the 11th case brought over economic espionage under a 1996 law, according to the US justice department.
Last year the US indicted five Chinese military officers for stealing information from energy, steel and aluminium companies, as well as trade unions.
Washington has long accused China of cyberspying in order to benefit Chinese companies, while Beijing frequently says it is itself a victim of hacking.
China is increasingly concerned about US cyberspying and has ordered many government departments to avoid using foreign technology.
"The Chinese government firmly opposes and combats thefts of trade secrets, in accordance with law," foreign ministry spokesperson Hong said. "As for this case, we are still checking on the details."
In a scheme that allegedly dates back to 2006, the six are accused of stealing trade secrets relating to so-called FBAR technology from companies two of them worked for, California-based Avago Technologies and Massachusetts-based Skyworks Solutions. It enables mobile phones and other devices to filter radio signals and improve performance.
According to the indictment a Chinese company set up as a joint venture between Tianjin University's investment arm and individuals including some of the defendants, ROFS Microsystems, manufactured rival products.
David Johnson, FBI special agent in charge in San Francisco, called the scheme a "methodical and relentless effort by foreign interests to obtain and exploit sensitive and valuable US technology through the use of individuals operating within the United States".
Zhang, 36, is a former Skyworks employee and a full professor at Tianjin University.
"We know about academic exchanges and research, but we haven't seen any evidence that these professors were spies," said a man in the Tianjin University propaganda department surnamed Feng. "We don't have anything to do with spying."
Zhang, arrested at Los Angeles International Airport, appeared before a US magistrate on Monday who ordered him held and transported to San Jose to face the charges.
Calls to ROFS Microsystems by AFP were not answered.