(Adds background and AMA statement in paragraphs 5 to 8)

March 7 (Reuters) - UnitedHealth expects to restore disrupted services for medical claims and payments platforms by mid-March, the company said late Thursday, as it grapples with the fallout of a hack that crippled its Change Healthcare tech unit late last month.

United's Change Healthcare unit is a vital lynchpin in the complex U.S. system for making and clearing insurance claims. The disruptions also impacted electronic pharmacy refills.

While its pharmacy operations returned online on Thursday, UnitedHealth said its payment platform will be operational on March 15, and its medical claims network will be restored on March 18.

The cyberattack on Feb. 21 at Change Healthcare was perpetrated by hackers who identified themselves as the "Blackcat" ransomware group, impacting doctors and medical practises across the U.S. healthcare system.

Many doctors depend on the system to verify insurance coverage, file claims and get paid, sparking a campaign by hospitals and doctors for the U.S. government to provide financial relief as it did during the COVID-19 pandemic.

"The prospect of a month or more without a restored Change Healthcare claims system emphasizes the critical need for economic assistance to physicians, including advancing funds to financially stressed medical practices," U.S. doctors advocacy group the American Medical Association's (AMA) President Jesse Ehrenfeld said in a statement.

On Tuesday,

the U.S. government said

it would push its Medicare contractors to provide flexible payment terms.

AMA and the American Hospital Association (AHA) have said the government support did not go far enough. (Reporting by Rishabh Jaiswal and Pratik Jain in Bengaluru; Editing by Rashmi Aich and Tasim Zahid)