South Korea's customs authorities raided the headquarters of Korean Air on Wednesday over allegations the company violated foreign exchange laws in a widening probe into the chairman's family.

The Korea Customs Service(KCS) said some 40 officials were dispatched to secure documents and hard disk drives at the airline's main office in western Seoul.

Customs officials are reported to have become suspicious that the airline may have violated foreign exchange laws while investigating allegations of smuggling and tax evasion by Chairman Cho Yang-ho's family.

Since last month, the customs agency has raided the residences of the Cho family and offices of Korean Air regarding allegations of smuggling of luxury goods without paying duties.

The Cho family is under a series of investigations after the chairman's youngest daughter, Cho Hyun-min, a former executive of Korean Air, was accused of assaulting an ad agency official.