Novosibirsk chemist Oleg Korobeinichev, who has ties with U.S. and European research institutes, is under investigation on suspicion of divulging state secrets, local prosecutors said Friday.

The case is the latest in a growing number of investigations involving researchers with foreign contacts.

The Federal Security Service, or FSB, which is investigating the case, has not filed any charges, said Natalya Markasova, an aide to the chief prosecutor for the Novosibirsk region, the Regnum news agency reported. Korobeinichev remains free, she said.

The prosecutor's office would not provide any further information about the case, including when the investigation began and what had raised suspicions, saying that all files in the case were classified, RIA-Novosti reported.

Korobeinichev heads a laboratory that studies flames and combustion at the Institute of Chemical Kinetics and Combustion, part of the Siberian branch of the Russian Academy of Sciences.

Reached at his laboratory Friday, Korobeinichev declined comment. "I am sorry, I don't have time now," he said. He added that he did not know when would be a good time to talk. But in comments carried by Interfax on Friday, he said he was unaware of the case and described the news reports as rumors.

The FSB's spokeswoman in Novosibirsk, Irina Zebrova, could not be reached, but she told RIA-Novosti that "we are not giving any comment about this issue." An FSB spokesman in Moscow declined immediate comment and asked for questions be faxed to him.

Korobeinichev's laboratory has built contacts or cooperated with a number of foreign research and educational centers, including Cornell University in Ithaca, New York; the National Institute of Standards and Technology, a U.S. Commerce Department agency based in Gaithersburg, Maryland, and Boulder, Colorado; the New Jersey Institute of Technology; and Cambridge University in Britain, according to the laboratory's web site. Korobeinichev directed two projects at his laboratory for the U.S. Army Research Office, which funded the projects, the web site said. The projects -- one of which was completed in August, while the other began in October -- studied the performance of various fuels, it said.

Korobeinichev is an associate fellow of the American Institute of Aeronautics and Astronautics, based in Reston, Virginia, according to the web site of Novosibirsk State University, where Korobeinichev is a professor.

Korobeinichev's case appears to be similar to others that were opened against researchers after they worked with foreign colleagues, said Alexander Petrov, head of Human Rights Watch's Moscow office, and Lev Ponomaryov, head of the For Human Rights group.

They accused the FSB, which usually supervises foreign ties at research institutes, of not making efforts to prevent scientists from becoming involved in activities that could be interpreted as espionage but rather waiting so that agents could open high-profile investigations and win promotions for their efforts.

In addition, keeping the files secret in the Korobeinichev case echoes a ploy used in previous cases, which were closed to the public and did not take into account independent assessments of whether the information that researchers shared with their foreign counterparts was sensitive, Ponomaryov said.

A separate investigation is under way into Igor Reshetin, the former director of Tsniimash-Export, a rocket and space technology company based in the Moscow region town of Korolyov, whom the FSB accuses of delivering sensitive technology to China in violation of state export controls. Oscar Kaibyshev, the former director of the Institute for Metal Superplasticity Problems, is on trial in Ufa on charges of exporting to South Korea dual-use technologies that can be used in building weapons of mass destruction. In 2004, Igor Sutyagin, an arms control researcher from the Kaluga region, was convicted of treason on charges of selling sensitive information on nuclear submarines and missile-warning systems to a British company suspected of being a CIA cover. Earlier, Krasnoyarsk physicist Valentin Danilov was found guilty of selling classified information on space technology to China.