AMSTERDAM (Reuters) - Telecoms group America Movil (>> America Movil SAB de CV) launched a sale of up to 2.5 billion euros ($2 billion pounds) worth of bonds exchangeable for KPN (>> KONINKLIJKE KPN) shares, leading to a possible exit by the Dutch firm's largest shareholder, after three difficult years.

In 2013 America Movil supported a hefty rights issue by KPN but failed in a full takeover attempt and reduced its stake.

If the bonds are exchanged, America Movil will have sold the majority of its 21.1 percent stake in KPN in 2020. However, the terms also provide it with an option to call the bonds if KPN shares rise sharply.

"America Movil has received cash today for the value of that stake, then they look five years out, and if the share price of KPN does absolutely nothing then that's a great position for them," said Justin Craib-Cox, convertible bond fund manager at Aviva Investors.

"This is a pretty neat and easy disposal without having to sell off a large chunk of shares at a discount in the market."

KPN shares, which have risen 29 percent so far this year, were down 4.5 percent early on Wednesday, as the deal makes another offer for all of KPN by America Movil less likely.

On average, Mexican group America Movil, owned by Carlos Slim, paid about 3.24 euros a share for its Dutch stake, including stock bought as part of the rights issue in 2013.

KPN's shares traded around 3.35 euros on Wednesday but the euro has fallen against other major currencies since KPN's rights issue, making it unclear whether the group has broken even on the purchase.

A spokesman for KPN said the company had "taken notice" of Movil's move announced early on Wednesday.

America Movil bought a first stake in the Dutch operator in 2012 and, though KPN's board advised shareholders against tendering their stock, secured a near 30 percent share of the company and two seats on the board.

Since 2012, KPN has sold all of its foreign operations such as its German mobile unit EPlus and its Belgian unit BASE, exclusively focusing on the Netherlands.

Apart from its stake in KPN, America Movil owns a majority of Telekom Austria (>> Telekom Austria AG) and has operations throughout the Americas.

($1 = 0.9035 euros)

(Reporting by Toby Sterling and Sinead Cruise; writing by Robert-Jan Bartunek; editing by Philip Blenkinsop and Elaine Hardcastle)

Stocks treated in this article : KONINKLIJKE KPN, Telekom Austria AG, America Movil SAB de CV