The largest U.S. health insurer is expanding deeper into South America by spending about $2.8 billion to buy a health care provider and insurer that operates in Chile, Colombia and Peru.

UnitedHealth Group Inc. said Friday that it will start an offer next week to buy all outstanding shares of Empresas Banmédica. It expects to complete the deal in next year’s first quarter.

Minnetonka, Minnesota-based UnitedHealth covers nearly 45 million people in the U.S. and another 4 million people internationally. That includes business in Brazil, where the insurer offers health and dental benefits and hospital and clinical services.

U.S. health insurance is still its main business. It offers employer-sponsored commercial coverage and is a big provider of Medicare Advantage plans.

UnitedHealth said earlier this month that it would spend almost $5 billion to buy nearly 300 primary and specialty care clinics and some urgent care and surgery centers from DaVita Inc.