UnitedHealth Group Inc., the biggest U.S. health insurance company, is in talks to buy a stake or all of the Brazilian insurer and hospital operator Amil Participacoes SA, according to people familiar with the matter.

Acquiring all or part of Brazil's biggest managed-care company, which carries a market value of 9.01 billion reais ($4.47 billion), would give Minnetonka-based UnitedHealth access to a growing private insurance market in the world's second-biggest emerging economy. It also may generate more opportunities for UnitedHealth's Optum unit, which provides technology and consulting to health systems in India, China, the U.K. and elsewhere.

A deal may be announced as soon as next week, according to the people, who asked to remain anonymous because the talks are private. While Amil is also talking with other possible bidders, UnitedHealth has emerged as the likely buyer, the people said.

Brazil has "a sophisticated private-sector hospital system as well as a private insurance system that's ripe for expansion," said Sheryl Skolnick, a health care analyst at CRT Capital Group in Stamford, Conn.

Amil fell less than 1 percent to 24.99 reais in Sao Paulo trading Thursday after gaining 49 percent in the last 12 months, amid speculation about a potential deal. UnitedHealth rose 2 percent to close at $57.97 after increasing 36 percent in the past 12 months.

Amil has hired Credit Suisse Group AG to sell a stake in its business, according to a second person familiar with the talks.

Amil "doesn't comment on speculation," the company said in an official statement. Tyler Mason, a UnitedHealth spokesman, said the company doesn't comment on rumors and speculation.

UnitedHealth has completed 24 deals in the last five years, for an average disclosed size of $1.13 billion.