Harry Potter publisher Bloomsbury has bought US academic publisher Rowman & Littlefield in a "game-changer" deal worth up to £65 million.

Chief executive Nigel Newton said the move will help accelerate expansion overseas. It is Bloomsbury's biggest acquisition to date and will see it become a leading academic publisher in North America.

Bloomsbury will pay $76m (£60m) in cash and up to $7m (£5m) held in escrow for Rowman & Littlefield, whose top authors cover academic arts, humanities and social sciences. The US group publishes thousands of nonfiction books and textbooks, both in print and digitally.

The combined business will publish nearly 100,000 titles between them, Bloomsbury said.

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"Their 40,000 academic titles added to ours will make us a significant US academic publisher, growing Bloomsbury's academic and digital publishing presence in North America, opening new markets and publishing areas to Bloomsbury, and is a key milestone in the delivery of our long-term growth strategy," Mr Newton said.

Bloomsbury, which also publishes cookbooks from chefs including Tom Kerridge, Gino D'Acampo and Paul Hollywood, recently revealed its biggest ever year of profit and sales.

Dan Coatsworth, an investment analyst for AJ Bell, said the latest takeover news shows Bloomsbury is taking steps to diversify its portfolio of authors and titles.

"Bloomsbury has come a long way from the days when its fortunes were almost completely tied to the Harry Potter franchise and today's acquisition of a US academic publisher accelerates the company's diversification strategy," he said.