WASHINGTON, April 26 (Reuters) - U.S. auto safety

regulators said Friday they have opened an investigation into

whether Tesla's recall of more than 2 million vehicles announced

in December to install new Autopilot safeguards is adequate.

The National Highway Traffic Safety Administration (NHTSA)

said it was opening an investigation after identified concerns

due to crash events after vehicles had the recalled software

update installed "and results from preliminary NHTSA tests of

remedied vehicles".

NHTSA also cited Tesla's statement "that a portion of the

remedy both requires the owner to opt in and allows a driver to

readily reverse it."

The agency said Tesla has issued software updates to address

issues that appear related to its concerns but has not made them

"a part of the recall or otherwise determined to remedy a defect

that poses an unreasonable safety risk."