Federal auto safety regulators came under scrutiny in a Senate hearing on Tuesday for their role in General Motors' failure to promptly report and recall cars with defective parts that led to at least 19 deaths, reported Reuters.

A report released by a House committee earlier on Tuesday said officials at the National Highway Traffic Safety Administration repeatedly failed to identify the potential problems with the faulty ignition switches and could have acted more quickly to catch the problem.

Senator Claire McCaskill, who chaired Tuesday's hearing, criticized the auto regulator for not pushing hard enough for information from GM by issuing subpoenas.

"That reflects obviously on an agency that is perhaps more interested in singing kumbaya with the manufacturers than being a cop on the beat," McCaskill said.

The regulator's deputy administrator, David Friedman, defended NHTSA, reminding the Senate committee that the agency sent investigators to examine crashes involving the now-recalled cars but that GM withheld information.

"NHTSA did not shrug," Friedman said.

According to the House panel's findings, NHTSA staff had the power and information that they needed to act over the faulty GM switches.

But they were hampered by "lack of knowledge and awareness regarding the evolution of vehicle safety systems they regulate," the report said.