While potentially safe, the provincial energy regulator in Alberta said it's not ready to lift a ban on a controversial steam-injection method for bitumen.

The Alberta Energy Regulator released results from an independent review of an assessment made by Canadian Natural Resources Ltd. of last year's seeps at its Primrose project, near the Cold Lake Air Weapons Range in Alberta.

The regulators said four so-called flow-to-surface events were reported last year, spoiling about 50 acres of land. The company's own report said a process called cyclical steam stimulation, or CSS, may have cracked open other subsurface layers, allowing oil to leak out of control from the site.

Jim Ellis, president of the Alberta regulator, said flow-to-surface events could be prevented if the right mitigation efforts are in place.

"That said, the AER is not prepared to approve a return to full operations at these sites until all potential risks are addressed and proper requirements are in place to avoid a similar incident," he said in a statement Tuesday. "This will require a gradual, step-by-step approach that allows us to manage those risks."

The AER placed restrictions on the steam injection method at the site in June 2013.

The regulator said cleanup efforts are ongoing, though all of the released bitumen, the viscous form of oil found primarily in Alberta, has been contained.