UnitedHealth Group Inc., a Minnesota-based managed care company with a large operation in Cypress, said Wednesday that it will buy the management arm of Irvine-based Monarch HealthCare, A Medical Group Inc.

A purchase price was not disclosed.

Monarch will fall under UnitedHealth’s Optum health services business unit, which is separate from UnitedHealth’s insurance operation.

The agreement is “a strategic relationship with Optum to support our physicians,” said Bart Asner, Monarch’s chief executive, in a report published on industry magazine Modern Healthcare’s Web site.

Optum shares Monarch’s commitment to bringing patients, doctors, hospitals and payers closer together, Larry Renfro, Optum’s chief executive, told Modern Healthcare.

Healthcare reform has fueled a trend toward integration and consolidation among doctors and hospitals.

Monarch includes about 2,300 doctors in Southern California, the majority of whom are in Orange County.

Optum, which also provides pharmacy benefit management and healthcare data, had previously taken over the management arms of two smaller area doctors’ groups, including the Memorial HealthCare Independent Practice Association.