Russian federal secret services FSB said Thursday it had detained two US citizens, one an employee of oil firm TNK-BP, on accusations of industrial espionage after a search of the company's headquarters, news agency Interfax reported, according to dpa. The FSB said the Zaslavsky brothers, who also hold Russian citizenship, were detained March 12 in "an attempt to secure classified information, which constitute commercial secrets, from a Russian citizen - an employee at a state oil and gas firm." The information could be used to procure a competitive advantage for foreign oil and gas companies to the detriment of Russian competitors in the CIS market, the FSB said in a statement Thursday. One of the named brothers heads a project for the British Council, whose legal status in Russia is sorely debated, while the other brother is an employee at the British-Russian oil firm TNK-BP, which is rumoured to be targeted for Russian state control. The FSB said that a raid of TNK-BP's Moscow headquarters on Wednesday was related to the investigation into charges of spying. Copies of documents from the Russian state government bodies, analytical reports reviewing Russia's energy resources and the business cards of employees of the US Central Intelligence Agencies (CIA) found during the search support suspicions of industrial espionage, according to the FSB said.