América Móvil, owned by billionaire Carlos Slim, said it would launch a tender offer to buy KPN shares at €8 each to increase its stake to 28% from 4.8%. The announcement ignited KPN's shares Tuesday as it would give investors a 23.4% premium to Monday's close.

"América Móvil has been evaluating the expansion of its operations to other regions outside the Americas. Geographic diversification is a key element that has brought great stability to cash flow, profitability and contributed to strengthening [the company's] credit ratings," it said in a statement to the Mexican securities regulator.

While European carriers look abroad for growth, outside buyers are increasingly chasing euro-zone assets as sovereign debt worries suppress valuations. KPN is trading on a forward price/earnings multiple of 8.5 times, compared with 12.4 times for América Móvil, according to Bloomberg data. The stake purchase would be Slim's first significant investment in Europe after several previous attempts to ring up the Continent and expand his telecommunications empire beyond the Americas.

Slim is reportedly following Hong Kong peer Li Ka-Shing in targeting a European telecom. Ka-Shing's Hutchison Whampoa Ltd. reportedly made an unsuccessful €2 billion offer for bankrupt Irish phone company Eircom Ltd. in recent days.

América Móvil said the stake increase would allow it to squeeze cost savings through roaming agreements and by sharing equipment, content and advertising.

"This should renew interest in European telecoms," wrote WestLB analyst Wolfgang Specht in a note. He has a buy rating on the stock.

KPN said it was aware of the move but made no other comment.

KPN's shares jumped 19.9%, or €1.28, in mid-day Amsterdam trade to €7.76. The stock had slid nearly 30% this year as CEO Eelco Blok, who took the post about a year ago, struggled to keep KPN on track.

The company in December became part of an investigation by the Dutch competition authority into price-fixing among phone companies and was also put under close supervision by the country's OPTA telecommunications regulator amid allegations of related infractions. KPN has denied any wrongdoing.

In January CFO Carla Smits-Nusteling unexpectedly quit, citing a disagreement over corporate governance.

KPN has said it's working to sell its Belgian Base discount cellular-services unit, which could bring in as much as €1.8 billion. The company is also in talks to sell its German broadcast towers, according to Der Spiegel.