Government scientists have detected an increase in emissions of an outlawed industrial gas that destroys ozone, potentially slowing progress in restoring the atmosphere’s protective ozone layer.

The scientists say that the increase is likely a result of new, unreported production of the gas, known as CFC-11, probably in East Asia. Global production of CFC-11, which has been used as a refrigerant and in insulating foams, has been banned since 2010 under an environmental pact, the Montreal Protocol.

The protocol was adopted in the late 1980s in response to studies that showed CFC-11 and similar gases, collectively known as chlorofluorocarbons, depleted atmospheric ozone. A layer of ozone in the stratosphere helps filter ultraviolet radiation from the sun that can cause skin cancer.

The Montreal Protocol, often hailed as the most successful international environmental agreement ever enacted, has led to declines in chlorofluorocarbons and an increase in stratospheric ozone. A full recovery of the ozone layer was expected by midcentury.