Irvine-based Mazda North American Operations said the North American rollout of its SKYACTIV-D diesel engine is no longer scheduled for the spring.

The automaker was originally expected to launch the engine in its Mazda6 sedan, but said that's being "further delayed.” It did not indicate a new launch date.

Instead, Mazda said in a release that "further development is required to deliver the right balance between fuel economy and Mazda-appropriate driving performance."

The diesel engine does not use a nitrogen-oxide emissions-cleansing system, but the automaker said SKYACTIV-D still meets emission requirements without it.

More details will be released closer to the engine's launch, the company said.

The SKYACTIV-G gasoline engine is available in the Mazda3 and Mazda6 sedans along with the CX-5 crossover.