Rio de Janeiro, Oct 9 (IANS/EFE): UnitedHealth Group Inc plans to buy 90 percent of Brazil's largest health insurer, Amil Participacoes SA, for roughly $4.9 billion, the companies said Monday.

UHG, the leading health insurer in the US, will initially acquire about 60 percent of Amil from the current controlling shareholders and management, the firms said in a regulatory filing.

A public offer for the other 30 percent will come in 2013.

The agreement calls for Amil's founder, Edson de Godoy Bueno, to retain 10 percent of the company - he and partner Dulce Pugliese currently hold 70 percent - for at least five years and to remain the chairman and CEO of the Brazilian firm.

Bueno is also to acquire $470 million worth of shares of UHG, making him the US giant's largest shareholder, with an entitlement to a seat on the board.

The deal is subject to approval by Brazil's National Health Agency.

Besides providing prepaid health services to 5 million policyholders, Amil owns and operates 50 hospitals. The firm expects revenues of $5 billion in 2012.

The number of Brazilians with private health insurance increased from 35 million in 2005 to 48 million, which is still only about a quarter of the population.