South Korea's Lotte Group said Monday four of its retail stores in China were closed after inspections by authorities, as Seoul protests at discriminating action by China after Lotte agreed to provide land for a U.S. missile defense system.

China is the biggest overseas market for Lotte Group, South Korea's No. 5 conglomerate, generating annual sales of a just over 3 trillion Korean won ($2.60 billion) in 2015.

A Lotte Mart spokesman said the four stores, in Dandong, Changzhou and two other locations, were closed last week after the inspections, but could not provide further details. Lotte Mart had about 115 stores in China as of January.