Two U.S. Navy sailors have been arrested on charges of providing sensitive U.S. military information to China in exchange for money in what the Justice Department called a relentless effort by China to get U.S. secrets.

Jinchao Wei was the first person ever charged with espionage in the San Diego district, U.S. Justice Department officials said at a news conference. Petty Officer Wenheng Zhao, 26, of Monterey Park, California, was charged with conspiracy and receipt of a bribe by a public official in Los Angeles.

Both men are Chinese-born naturalized U.S. citizens. It wasn¡¯t immediately clear whether they have retained lawyers.

Wei sent documents to China and received thousands of dollars, providing the country information on potential vulnerabilities of ships, photos of military hardware and scores of technical manuals, placing the safety of U.S. sailors in jeopardy, prosecutors said.

¡°The charges demonstrate the PRC¡¯s determination to obtain information that is critical to our national defense by any means so it can be used to their advantage,¡± Matthew Olsen, head of the Justice Department¡¯s national security division, told reporters Thursday during a news conference in San Diego.

Liu Pengyu, a spokesperson for the Chinese embassy in Washington, said he wasn¡¯t aware of the details of the case, but cautioned about jumping to conclusions.

¡°In recent years, the U.S. government and media have frequently hyped up cases of ¡®espionage¡¯ related to China, many of which later proved to be unfounded,¡± Liu said in a statement. ¡°China firmly opposes the U.S. side¡¯s groundless slander and smear of China.¡±

Michael Casey, Washington¡¯s pick to lead counterintelligence efforts, said the U.S. faces ¡°unprecedented¡± threats from China, Russia and other foreign actors during a Senate confirmation hearing in July.

¡°China, among all such nations, stands apart in terms of the threat that its government poses to the United States,¡± Olsen said.

Federal Bureau of Investigation Director Christopher Wray said last year that the FBI opens a new counterintelligence case against China every 12 hours on average. China¡¯s foreign ministry routinely denies U.S. allegations of state-sponsored espionage.