China’s largest brokerage, CITIC Securities, said on Sunday that it could not contact its two top investment bankers Chen Jun and Yan Jian lin. Chen is head of the company’s investment banking sector and Yan is head of global investment banking, Citic said in a statement filed with Hong Kong Exchanges & Clearing . WATCH: China trading probe hits big broker CITIC Securities Mainland Chinese business media Caixin on Friday reported the pair had been detained and are either under investigation or assisting in an investigation by authorities. So far six of Citic’s eight executive committee members are missing. Four executives were taken away by police earlier this year, including company president Chen Boming, who is in charge of the brokerage’s daily operations. Citic’s Hong Kong-listed shares closed down 0.3 per cent at HK$17.96. READ MORE: China’s Citic Securities announces retirement of chairman Wang Dongming Several top Chinese brokerages are believed to be the subject of a government probe into insider trading in the wake of market mayhem during the summer. Guotai Junan International, a Hong Kong subsidiary of Guotai Junan Securities, one of China’s largest brokerages, said last month it had been unable to reach its chairman Yim Fung. Citic said in Sunday’s filing that some of their employees have returned to their office after assisting investigators.