Private equity firm MBK Partners and Young Poong Inc. raised their offer price to buy a stake in Korea Zinc Inc., according to a regulatory filing Thursday, amid an intensifying battle for control of the world's largest refined zinc producer.MBK Partners, in cooperation with Young Poong, which is the biggest shareholder of Korea Zinc, has launched a public tender offer to purchase a maximum 14.6 percent stake in the smelter for 660,000 won (US$495) per share.But MBK Partners' special purpose company, Korea Corporate Investment Holdings, said in a regulatory filing that it raised the offer price to 750,000 won per share.The move had been expected because the tender offer has sent shares of Korea Zinc to a record high.Shares of Korea Zinc rose 0.72 percent to close at 704,000 won Wednesday.Currently, Young Poong holds a 33 percent stake, while Korea Zinc and its owner family collectively own 18 percent.Source: Yonhap News Agency