Iraq's special forces say they have begun an assault against the Islamic State group on a sprawling military base south of Mosul that's adjacent to the city's airport.

Two Iraqi special forces officers say their troops have reached the Ghazlani base on the city's southern edge on Thursday morning and that clashes there are underway.

A federal police officer says his forces are also pushing toward the Mosul airport. All officers spoke on condition of anonymity because they are not authorized to talk to reporters.

The advances come days after Iraqi forces officially launched the operation to push IS out of Mosul's western half.

The operation to retake Iraq's second largest city was officially launched in October and in January its eastern half was declared "fully liberated."