UnitedHealth Group Inc. is failing to meet terms of a $20.5 billion military contract, causing lingering delays to medical care, a Pentagon official said.

The backlogs occurred after Minnetonka-based United­Health took over the contract last month from TriWest Healthcare Alliance Corp., according to the Defense Department. The agreement is for coordinating care in the western region of the military's Tricare health system.

UnitedHealth "continues to be unable to comply with the requirements of their contract," Jonathan Woodson, assistant secretary of defense for health affairs, said in a memo dated Thursday. The result is that beneficiaries are prevented "from obtaining timely access to specialty care and potentially causing them to suffer harm," he said.

UnitedHealth is "deploying the full resources of the company to ensure that beneficiaries receive the care and service they deserve," Lori McDougal, chief executive officer of the firm's military and veterans unit, said in a statement.

McDougal said the company is also "making progress in clearing pending referrals and authorizations."