SEOUL (Reuters) -Korea Zinc on Friday raised the purchase price and size of its tender offer, intensifying a battle between its two founding families to control the world's biggest zinc refiner.

Korea Zinc said it has raised the tender price by 7% to 890,000 won ($659) each and increased the number of shares it plans to acquire by 21% to 3,623,075 shares, valuing the tender offer at 3.2 trillion won ($2.4 billion).

The move is "the only way to thwart hostile M&A by MBK Partners and Young Poong," Korea Zinc said in a statement.

The offers tops the offer of 830,000 won per share from MBK and Young Poong.

MBK said on Wednesday it would not raise its offer prices for Korea Zinc or affiliate Young Poong Precision, citing concern that a bidding war would put a financial burden on Korea Zinc.

South Korea's Financial Supervisory Service (FSS) on Tuesday ordered a probe into tender offers for Korea Zinc shares to monitor for any unfair trade practices.

Korea Zinc shares fell 1% to 781,000 won each in morning trade. The latest tender offer by Korea Zinc has a deadline of Oct. 23.

Jerico Partners, the investment vehicle of Korea Zinc's chairman Yun B. Choi, on Friday raised its offer for Young Poong Precision by 16.7% to 35,000 won per share.

The Choi family's offer tops a sweetened offer from MBK of 30,000 won per share for Young Poong Precision, which holds a minority stake of 1.85% in Korea Zinc.

Shares of Young Poong Precision were trading down 6% at 29,300 won.

(Reporting by Heekyong Yang, Hyunjoo Jin and Joyce Lee; Editing by Jacqueline Wong, Sonali Paul and Tom Hogue)

By Heekyong Yang