NEW YORK • Burger King's mascot, The Burger King, is seeking a truce, albeit temporary, with McDonald's mascot Ronald McDonald.

The fast-food chain is reaching out to its long-time competitor with an unusual proposal: Create a hybrid of each company's signature burger - Big Mac and Whopper - and then sell it at a pop-up restaurant in Atlanta for one day.

The profits will go to an organisation that promotes world peace.

In full-page advertisements running in The New York Times and the Chicago Tribune yesterday, Burger King, a perennial also-ran in the burger races, has asked McDonald's, its battered but still potent arch-rival, to join forces.

Call it "McWhopper" diplomacy.

"We are being completely transparent with our approach because we want them to take it seriously," Mr Fernando Machado, senior vice-president for global brand management at Burger King, said in a statement. "It would be amazing if McDonald's agrees to do this."

Burger King created a website, mcwhopper.com, that includes a proposed recipe for the McWhopper. The sandwich has six ingredients from the Big Mac (including special sauce, all-beef patty and cheese), and six from the Whopper (flame-grilled patty, onion, pickles, among others).

One sticking point might be the ketchup. McDonald's famously stopped using Heinz ketchup when private equity group 3G Capital bought the company, and Burger King has suggested using it on the McWhopper. And there is no word about who will supply the fries.

Burger King has also mocked up hybrid employee uniforms and packaging for the burgers. It proposes opening the pop-up store on Sept 21, set by the United Nations as the day to celebrate world peace, in a carpark between a McDonald's outlet and a Burger King outlet.

"Corporate activism on this scale creates mass awareness, and awareness creates action and action saves lives," Mr Jeremy Gilley, founder of Peace One Day, said in a video posted on the mcwhopper.com website.

No Burger King executive was available for comment, but Mr Machado urged McDonald's to help "make history and generate a lot of noise around Peace Day". McDonald's declined to comment.

Burger King is now part of Canadian-based firm Restaurant Brands International, which was created by 3G Capital when it merged the burger chain with Tim Hortons, a Canadian restaurant chain.

The new owner cut costs, quickly improving the chain's financial performance. Improving sales proved a bigger challenge and, for a time last year, Burger King ceded its position as the world's No. 2 burger chain to Wendy's.

NEW YORK TIMES, BLOOMBERG