Dec 12 (Reuters) - South Africa's Northam Platinum on Monday raised the cash part of its takeover offer for Royal Bafokeng Platinum by 7 billion rand ($398 million), to try to increase its appeal against a rival bid from Impala Platinum.

The maximum cash value of the offer now stands at 17 billion rand, up from 10 billion rand, Northam said, adding the share component had been reduced by 7 billion rand to keep the total offer at the 172.70 rand per share proposed last month.

Northam acquired a 33% stake in RBPlat in November 2021 after Impala announced its plans to buy RBPlat, triggering a bidding war that has gone on for months.

Both Northam, which currently owns 34.52% of RBPlat, and Impala, the biggest shareholder with 40.71%, are seeking to add RBPlat's large, shallow, high-quality assets to their portfolios.

Impala is one of the world's top five platinum producers. Its output totalled 2.27 million ounces of platinum group metals in the 12 months ended June 30.

Northam wants to add RBPlat's output to the 716,488 ounces it produced in 2021 as part of its strategy to reach 1 million ounces. RBPlat produced 467,000 ounces in 2021.

($1 = 17.5716 rand) (Reporting by Pushkala Aripaka in Bengaluru and Nelson Banya in Harare; Editing by Sherry Jacob-Phillips and Mark Potter)