WASHINGTON, Oct 18 (Reuters) - The U.S. auto safety regulator on Friday opened an investigation into 2.4 million Tesla vehicles equipped with the automaker's Full Self-Driving (FSD) software after four reported collisions, including a 2023 fatal crash.

The National Highway Traffic Safety Administration's (NHTSA) preliminary evaluation is the first step before the agency could seek a recall of the vehicles if it believes they pose an unreasonable risk to safety.

The new scrutiny of the advanced driver assistance system comes as Tesla CEO Elon Musk looks to shift Tesla's focus to self-driving technology and robotaxis as it faces growing competition and weak demand in its auto business.