GM is also under investigation by the US Department of Justice, Congress, the US Securities and Exchange Commission and several states for its handling of the faulty ignition switch, which engineers first discovered in 2001. GM has been criticized for failing to detect the faulty part and for not recalling the vehicles before this year.

GM recalls 1.5m more vehicles, totaled 6.3m

GM to pay $35m fine for delaying recalls

The automaker expects to complete an internal probe of its handling of the issue within the next two weeks.

The largest of the four new recalls announced on Tuesday covers more than 1.5 million full-size crossovers from model years 2009 through 2014 to replace potential defective seat belts. GM has told dealers to stop selling the newer models until they are repaired.

The other large recall covers almost 1.1 million older-generation mid-sized sedans with 4-speed automatic transmissions where a shift cable could wear out. The total number of vehicles affected by this recall outside the US market was not yet available. This is an expansion of a previous Saturn Aura recall.

GM also put a stop-sale order on the 2015 Cadillac Escalade and Escalade ESV full-size SUVs, recalling about 1,500 vehicles because the passenger side air bags may not deploy properly in an accident. The company said it has emailed the 224 customers who had taken delivery of the vehicles, telling them not to let passengers sit in the front passenger seat until the repair has been made.

The company also recalled 58 heavy-duty versions of its 2015 full-size Chevy and GMC pickup trucks in the United States for potential fire issues.