A US corporate due diligence firm says its five employees detained by China's national security authorities have been released after two years of detention.



The move is believed to be part of Beijing's efforts to ease worries among foreign businesses and attract investment.



The Mintz Group says all the detained employees at its Beijing office, all Chinese nationals, have been freed as of Tuesday.



A spokesperson of the firm told NHK, "We are grateful to the Chinese authorities that our former colleagues can now be home with their families."



Western media report the Mintz staff were detained by Beijing's public security bureau following a raid on the firm's office in the Chinese capital in March, 2023.



Under the national security policy of President Xi Jinping's leadership, the authorities have cracked down on espionage since 2023, including a case involving an official at a foreign consulting firm.



This is causing concerns among overseas businesses.



Last year, direct investment into China plunged more than 90 percent from the previous year.