The European Aviation Safety Agency (EASA) later said it would be grounding all flights involving the plane, widening a prohibition to all EU member states.

Germany had earlier banned flights by the Boeing 737 MAX 8 in its own national airspace, becoming one of several countries to do so after last Sunday's Ethiopian Airlines crash.

"Safety comes first," said German Transport Minister Andreas Scheuer, shortly after Germany-based travel operator TUI said it was halting flights with the aircraft across all of the group's airlines.

"Until all doubts have been cleared up, I have ordered that German airspace be closed to all Boeing 737 MAX aircraft with immediate effect," Scheuer told German NTV television.

France's DGAC aviation agency had already barred such flights through its airspace Tuesday, along with Britain's Civil Aviation Authority.

EASA noted that the "exact causes" of a crash of a 737 MAX aircraft operated by Indonesian airline Lion Air in October, in which 189 lives were lost, were still being investigated.

"Since that action, another fatal accident occurred," EASA said, referring to Sunday's crash.

Read more: US demands changes to 737 MAX 8

Hanover-based TUI, which had operated 15 such aircraft in British and Benelux nation airspace, said it was following a MAX flight prohibition issued by Britain's Civil Aviation Authority.

TUI said its passengers booked to fly Tuesday on such aircraft were being informed of travel rearrangements.

Read more: Boeing 737 MAX: a plane of compromise

Only last Thursday, TUI had announced plans to introduce six "fuel efficient" MAX aircraft operating from German airspace, starting on April 13 from Hanover to Las Palmas in the Canary Islands.

Meanwhile, Boeing insisted it had "full confidence in the safety of the MAX," adding that the US authority FAA had not mandated "any further action at this time."

String of groundings

More than a dozen other countries have also grounded the 737 MAX in response to the two crashes. These include China, India, Indonesia, Singapore, Malaysia, Serbia, New Zealand, Australia, Ethiopia, Namibia, Egypt, Turkey, Lebanon, Kuwait, Oman and the United Arab Emirates.

Read more: Why do airplanes stall and why is it so dangerous?

On Monday in the wake of the Ethiopian, the US Federal Aviation Authority (FAA) issued a "continued airworthiness notification" for the 737 and detailed a series of design changes mandated by Boeing after last year's crash in Indonesia.

Boeing said had been working to enhance flight control software that would be deployed across the 737 MAX fleet in the coming weeks.

Major airlines from North America have said they will keep flying the 737 MAX, the new variant of the 737, a workhorse for airlines for decades around the globe.

But that decision has sparked protests from two major labor unions.

The Association of Professional Flight Attendants (APFA) and the Transport Workers Union (TWU) called on American Airlines and Southwest, the two largest airlines that use the 737 MAX, to ground their aircraft until more was known about the cause of the Ethiopian crash.

The 157 victims killed in Sunday's Ethiopian tragedy came from more than 30 different nations, and included nearly two dozen United Nations staff bound for Nairobi, the venue this week of a UN conference.

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ipj/rc (dpa, Reuters, AFP)