The deadline to file claims under General Motors Co's faulty ignition-switch compensation program has been extended by one month to Jan. 31, said Kenneth Feinberg, the program's administrator, reported Reuters.

Feinberg's office on Monday updated its list of claims submitted, saying it had approved compensation for the families of 33 victims killed in GM cars with faulty ignition switches.

Notice of the deadline extension was sent to about 4.5 million current and previous owners of eligible vehicles, Feinberg said in a statement. An extension of a further month was being implemented "out of an abundance of caution," he said.

GM said it agreed with the extension of the deadline.

"Our goal with the program has been to reach every eligible person impacted," the company said in a statement.

Democratic Senator Richard Blumenthal of Connecticut, an outspoken critic of GM's handling of its ignition-switch problems, said the extension was "inadequate."

In a statement, Blumenthal said the compensation fund deadline should either be eliminated or substantially modified.

"GM should either commit to waiving its bankruptcy shield in all pending legal actions, or permit all victims who qualify for the fund to postpone their acceptance of their compensation until the completion of the Department of Justice investigation into GM’s possible criminal actions," he said.

Last week, a car-safety advocate urged a more active approach to finding cases of injury or death. Clarence Ditlow, executive director of the Center for Auto Safety, asked Feinberg to expand outreach efforts and scour federal car-safety databases for accidents in recalled vehicles to determine whether the switch was to blame for additional injuries or deaths.

The program, GM Ignition Compensation Claims Resolution Facility, began accepting claims Aug. 1 and as of Friday had received 2,105 for deaths and serious injuries linked to the switch.

Shares of GM were up 1.6 percent at $32.29 in afternoon trading.