Dec 14 (Reuters) - Amgen Inc on Monday said it had reached a deal with British drugmaker GlaxoSmithKline to reacquire the sales rights to three of its products in 48 countries, including Australia as well as markets in Asia, South America and Europe.

The three Amgen drugs are the osteoporosis treatment Prolia; the related drug XGeva, used to prevent fractures in cancer that has spread to the bone, and Vectibix for advanced colorectal cancer.

Glaxo reported $111 million in combined sales in 2014 from the licensing of the three drugs, Amgen said.

Amgen will make undisclosed milestone payments to Glaxo upon signing and the successful transition of the products back to Amgen, after which the California-based biotech company will book all sales for the medicines, it said.

The territories include countries that Amgen sees as key international markets in which it is looking to expand business, including Brazil, China, Colombia, Hong Kong, Israel, Singapore, South Korea, Taiwan and Thailand.

Amgen expects to complete the transition in the majority of these emerging markets within a 12-month period. It expects the deal to add to its adjusted earnings beginning in 2017.

"This unique agreement with GSK allows Amgen to regain rights to three important growth products, and to directly serve more patients in key expansion markets," Amgen Chief Executive Robert Bradway said in a statement.

In extended trading, Amgen shares were flat at $158.11, unchanged from their earlier close on the Nasdaq.

(Reporting by Bill Berkrot, editing by G Crosse)