The Obama administration can't verify that Obamacare subsidies were withheld from customers who didn't pay their health insurance premiums, according to a new inspector general report released Wednesday.

The earnings-based subsidies go to low- to middle-income Americans to help make their premiums more affordable — but those customers are expected to pay a share out of their own pockets. But the Centers for Medicare and Medicaid Services doesn't have an effective process to ensure customers are covering their part of the bill, the Inspector General for the Department of Health and Human Services found.

Instead, CMS is relying on insurers selling the plans to verify that the customers are paying their premiums and are even eligible to receive them, the oversight agency said.

"CMS could not ensure that [advanced tax credit] payments made to [qualified health plan] issuers were only for enrollees who had paid their premiums," the agency wrote.

The inspector general has raised a number of similar concerns about Obamacare subsidies, recently finding that CMS is unable to ensure the subsidy payments made to private insurance plans are accurate. Republicans have seized on those concerns to highlight their doubts that there is proper oversight of money being handed out under President Obama's signature healthcare law.

Eligible Americans are in their third year of receiving Obamacare subsidies through the new online insurance marketplaces set up under the Affordable Care Act. This year's enrollment season ends at the end of January.

To ensure the subsidies go only to those who pay their premiums, the inspector general recommended that CMS establish its own verification process instead of relying on insurers.

In its response, the agency agreed that it should set up its own verification system.