Pharmacies across the U.S. are reporting delays and disruptions following a cyberattack on UnitedHealth’s technology unit, Change Healthcare.

Fox Business reported the problems began on Wednesday after a “suspected nation-state associated cybersecurity threat actor” gained access to Change’s system. Tennessee-based Change is a provider of healthcare billing and data systems.

“Change Healthcare is experiencing a cyber security issue, and our experts are working to address the matter,” according to the latest Change Healthcare statement posted on its website at 11:32 a.m. ET on Feb. 22. “Once we became aware of the outside threat, in the interest of protecting our partners and patients, we took immediate action to disconnect our systems to prevent further impact. At this time, we believe the issue is specific to Change Healthcare and all other systems across UnitedHealth Group are operational.”

The FBI, the Department of Health and Human Services, and the Cybersecurity and Infrastructure Security Agency are involved in the investigation, the statement said.

Fox News reported a variety of pharmacy chains were experiencing disruptions, including an inability to process insurance claims. Several pharmacy companies said customers could expect delays until the matter is resolved, Fox News said.

The incident started early Wednesday on the U.S. East Coast, though Change has not confirmed the nature of the attack or its origin.