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By Sriparna Roy

(Reuters) -Many pharmacies across the U.S. could not transmit insurance claims for their patients after UnitedHealth Group (NYSE:UNH)'s Change Healthcare (NASDAQ:CHNG) reported a hack earlier this week, the American Pharmacists Association said on Friday.

"This is resulting in delays in getting prescriptions filled," the association said in a statement.

The disruptions from the attack were expected to last at least through Friday, Change Healthcare, the healthcare billing and data systems provider, said on its status page.

APhA said pharmacies across the nation were reporting "significant backlogs of prescriptions," which they are unable to process.

On Thursday, a number of pharmacy chains, including CVS Health (NYSE:CVS) and Walgreens said the outage at Change Healthcare was having knock-on effects on their businesses.

Independent pharmacies also reported problems as the disruption entered its third day.

"I think whenever it first happened, we were told it, it may be resolved by today, but found that wasn't the case," Ashley Moose, owner and pharmacy manager of Moose Pharmacy in Monroe, North Carolina, said in an interview.

Moose added that she had received an email from UnitedHealth's Optum unit saying the company was trying to resolve "transmission issues".

Change Healthcare, UnitedHealth's technology unit, is part of the Optum business through which the company offers several healthcare services.

In its statement, APhA urged patients to check with their respective pharmacies before heading there, and noted that not all pharmacies were affected.

"This situation may take several days to resolve, so in the meantime we would ask the public to please keep in mind the incredible extra stress this situation places on pharmacies and pharmacy personnel," said association CEO Michael Hogue.

Hack against Change Healthcare 'resulting in delays', says American Pharmacists Association