FRANKFURT—K+S AG on Friday said it rebuffed another unsolicited takeover approach from Canadian rival Potash Corp of Saskatchewan Inc. that valued the German salt and fertilizer company at €7.9 billion ($8.63 billion).

The company said the proposed takeover price was unchanged at €41 a share. However, Potash's new overture came with a business combination agreement—more concrete than the initial informal approach—that included commitments on job security, according to people familiar with the matter.

The move increases pressure on K+S, which rejected Potash's earlier approach in July, saying it undervalued its projects and products and could compromise jobs.

K+S shares rose more than 1% to trading above €37 in response to the news.

A combination of K+S and Potash, if successful, would be the largest mining deal since Glencore International PLC's takeover of Xstrata PLC for almost $30 billion in February 2012. Both companies mine potash, a fertilizer, and a tie-up would create a giant that could control as much as 30% of the global market.

Bankers and analysts have said that Potash is especially keen on a mine K+S is developing in the western Canadian province of Saskatchewan because it would help the company gain control over production capacities and price power in negotiations with farmers.

Potash Chief Executive Jochen Tilk said in late July he believes a combination with K+S would benefit the companies and that he remains interested in holding talks with K+S management because a merger would "enhance the breadth of each company's respective portfolio, improve cash flow capabilities and provide a more stable operating environment."

Mr. Tilk, a German, added that Potash, would seek a friendly acquisition of K+S and that he was willing to make a binding commitment to ensure that K+S operates as a separate brand and keeps its headquarters in Germany.

He stressed that Potash is committed to building K+S's $4.1 billion potash mine in south Saskatchewan, the first such mine to be built in the Canadian province in 40 years. The Legacy mine is expected to start production late next year and reach full capacity of 2.86 million metric tons by 2023.

Write to Eyk Henning at eyk.henning@wsj.com and Neetha Mahadevan at neetha.mahadevan@wsj.com

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