The battle for control of Lotte Group, South Korea's fifth-largest conglomerate, escalated as the founder's elder son said he will seek to oust his younger brother and executives of a holding firm that fired the group patriarch this year.

The Lotte founder's eldest son, Shin Dong-joo, has been locked in a bitter succession feud with his younger brother, Lotte Group chairman Shin Dong-bin, who had gained the upper hand after shareholders in the holding firm supported him in August.

A prolonged fight could hurt Shin Dong-bin's attempts to revamp the retail-to-construction conglomerate's opaque shareholder structure - attempts which are set to include an IPO for its hotel unit that analysts say may have a market value of up to 20 trillion won ($17.3 billion).

Shin Dong-joo said in a statement on Thursday that he will represent their 93-year-old father in lawsuits seeking to claim control of the group.

The lawsuits, planned in Japan and South Korea, will contest Lotte founder Shin Kyuk-ho's removal from key positions in Lotte Holdings, according to a statement by Shin Dong-joo that was read by his wife at a media briefing in Seoul.

Until last year, Lotte's operations had been unofficially divided between the two brothers, with the younger running the much bigger South Korean operations and the elder running the Japan businesses.

Lotte Group, representing Shin Dong-bin, said in a statement that Shin Dong-bin's management control of Lotte in Japan and South Korea had been decided through due process, and said it was doubtful that founder Shin Kyuk-ho's participation in the lawsuit was according to his true intentions. It has previously said that the founder was having trouble "making judgements".