Prosecutors said Tuesday they have launched an investigation into Hyosung Group on suspicion that the country's 26th-largest conglomerate evaded a massive amount of taxes.

The probe comes after the country's tax agency had filed a charge against the group's chairman, Cho Suck-rai, 79, with the Seoul Central District Prosecutors' Office for allegedly leading the tax evasion scheme through various illegal methods.

According to the sources at the National Tax Service (NTS), which conducted a special audit into the group in May, the family-run conglomerate had evaded corporate tax worth 1 trillion won ($900 million) for the past 10 years since 1997 through an accounting fraud.

Chairman Cho is additionally accused of holding shares under borrowed names since the 1990s to evade transfer tax and income tax worth more than 100 billion won, they added.

The NTS has already banned Cho and two others -- the chairman's key aide, whose identity has been withheld, and Vice Chairman Lee Sang-woon -- from leaving the country pending investigation results, they said.

Prosecutors said they will soon summon Hyosung Group officials for questioning after reviewing relevant data from the NTS.

The group, with more than 11 trillion won in assets, has business mainly in the fields of energy and heavy industry.

One of the chairman's nephews is a son-in-law of former President Lee Myung-bak.

According to industry sources, two of the chairman's sons are competing to secure stakes in the group's flagship company Hyosung Corp., a textile and heavy machinery maker, in a bid to gain control of the group's management.(Yonhap News)