incompetence led to delayed recall

General Motors says 15 employees have been sacked after a delayed recall of cars with a defective ignition problem that is blamed for 13 deaths.

GM is to release the results of a probe into the company's response to an ignition problem. (AAP)

GM CEO Mary Barra says 15 employees have been fired over the company's recent ignition switch recalls.

Barra made the announcement on Thursday as she released an internal investigation into the recall of 2.6 million older small cars for defective ignition switches.

Barra called the internal investigation into its recent ignition switch recall is "brutally tough and deeply troubling".

It took GM more than a decade to report the switch failures, which it blames for 13 deaths.

In a town hall meeting at GM's suburban Detroit technical centre, Barra says attorney Anton Valukas interviewed 230 employees and reviewed 41 million documents to produce the report, which makes recommendations to avoid future safety problems.