A data center serving the Obamacare Marketplace websites in 14 state-operated exchanges as well as the nationwide HealthCare.gov site went down Sunday, blocking all online health insurance sign-up operations throughout the country.

The data center, operated by Verizon's Terramark division, experienced a connectivity problem early Sunday that severed access to the federal databases needed for personal identity and citizenship verification. A spokesperson for the Department of Health and Human Services (HHS) said the outage occurred during routine planned maintenance.

"Our engineers have been working with HHS and other technology companies to identify and address the root cause of the issue," Verizon spokesman Jeff Nelson said.

Meanwhile, the administration has vowed to fix by Nov. 1 the various problems with the HealthCare.gov site that have prevented people from signing up for health care and sometimes sending faulty data to insurance companies from those who do succeed in signing up.