March 20 (Reuters) - UnitedHealth Group said on Wednesday its unit Change Healthcare's cloud-based services for handling medical claims were completely rebuilt and restored, about a month after a cybersecurity attack on the subsidiary crippled healthcare in the United States.

Amazon's cloud services for two of Change Healthcare's applications were restored from backups and cleared by their cybersecurity partners, the insurer said.

Change's Assurance and Relay Exchange are cloud-hosted applications that rely on authentication services. Assurance is a medical claims and remittance management software, while Relay Exchange acts as a clearinghouse which checks insurance claims for errors.

The services were "completely rebuilt" with the help of cybersecurity firm Palo Alto Networks and reviewed by Google-owned peer Mandiant, the company said, adding these were being monitored by at least two scanning services.

"We have taken every precaution and safety measure and implemented several rounds of security protocols — both internally and with our third-party partners — to ensure complete confidence in the platform," UnitedHealth said.

Change Healthcare, which processes about 50% of medical claims in the U.S. for around 900,000 physicians, 33,000 pharmacies, 5,500 hospitals and 600 laboratories, was breached on Feb. 21 by a hacking group called ALPHV, also known as "BlackCat."

With about 1 in 3 U.S. patient records handled by Change's health technology offerings, the cyberattack sent shockwaves across the nation's healthcare system and is now under investigation by the government health department.

UnitedHealth said on Monday it will start releasing its medical claims software and it has advanced payments of over $2 billion so far to provide assistance to healthcare providers financially affected by the hack.

The company had also suspended paperwork required to get approval for insurance coverage for most outpatient services, as well as the review of inpatient admissions for government-backed Medicare Advantage plans, to help those impacted. (Reporting by Leroy Leo and Mariam Sunny in Bengaluru; Editing by Krishna Chandra Eluri)