US Democratic Senator Richard Blumenthal, who has called for the grounding of the aircraft since Monday, said the FAA took a right but "overdue" step.

"This step is right, but unacceptably overdue. Our nation should be leading, not lagging, in air safety. Strong, immediate scrutiny is necessary," Blumenthal tweeted, stressing that the US public deserve to know "when this possible defect was 1st known, what will be done about it & who is responsible."

Boeing issued a statement saying it was supporting the temporary grounding "out of an abundance of caution."

Boeing said Monday it is planning to make a safety upgrade to software that is to be deployed across the 737 Max fleet in the coming weeks.

Despite Sunday's air crash in Ethiopia, Boeing said that the 737 Max is "a safe airplane that was designed, built and supported" by its skilled employees.

Ethiopia said it would send the black boxes recovered from the crash site to France for analysis, which could provide crucial information about what happened.

The 737 Max is Boeing's most important aircraft type, generating about one third of the company's operating profit.

According to the FAA, there are 387 Boeing 737 Max 8 jets in operation at 59 airlines worldwide, 74 of which are registered in the United States.

Since debuting in 2017, the Max jets, which is a key part of Boeing's effort to compete with rival Airbus, have plunged the company into its worst crisis in years.

Boeing shares decreased sharply on Wednesday shortly after Trump's decision to ground Boeing 737 Max 8 and 9 jets, but pared losses later in the day and closed up 0.46 percent. By far this week, the stock fell more than 10 percent.

A Boeing 737 Max 8 plane of Ethiopian Airlines crashed on Sunday morning, killing all 157 passengers and crew members on board. The plane crash was the second fatal incident involving the same model in five months.