Britain, France and Germany joined a growing list of countries to ban Boeing 737 MAX planes from their airspace on Tuesday as airlines around the world grounded the jets following a second deadly accident in just five months.
On Sunday a new Ethiopian Airlines 737 MAX 8 went down minutes into a flight to Nairobi, killing all 157 people on board, from 35 countries.
In October, a Lion Air jet of the same model crashed in Indonesia, killing 189 -- but no evidence has emerged to link the two incidents.
The widening airspace closures puts pressure on Boeing, the world's biggest planemaker, to prove 737 MAX planes are safe as increasing numbers of fleets have been grounded.
Turkish Airlines was among the latest to announce it was suspending its 12 Boeing 737 MAX aircraft from flying from Wednesday, until "uncertainty" was clarified.
Low-cost airline Norwegian Air Shuttle, South Korea's Eastar Jet and South Africa's Comair also said they would halt flights, but the full extent of the impact on international travel routes was unclear.
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On Twitter, US President Donald Trump weighed in on the probe investigating the Ethiopian Airlines crash, writing: "Airplanes are becoming far too complex to fly." "Pilot are no longer needed, but rather computer scientists from MIT," he wrote, referring to the prestigious university in Massachusetts.
US carriers have so far appeared to maintain confidence in Boeing, which has said it is certain the planes are safe to fly.
US federal aviation authorities, the FAA, have not grounded Boeing 737 MAX 8 aircraft but have ordered the manufacturer to make design changes.
The move was not enough to reassure the UK Civil Aviation Authority, which said in a statement headlined "Boeing 737 MAX Aircraft" that it was banning the planes from UK airspace "as a precautionary measure".
Global air travel hub Singapore, as well as Australia, Malaysia and Oman were among the other countries to ban all 737 MAX planes from their airspace.
China, a hugely important market for Boeing, had already ordered domestic airlines to suspend operations of the plane on Monday, as did Indonesia.
Elsewhere Argentina's flag carrier also grounded five MAX 8 aircraft on Tuesday, as did airlines in countries including Brazil and Mexico.
But several airlines said they were not cancelling MAX 8 flights.
"The Boeing 737 MAX is a highly sophisticated aircraft," said India's SpiceJet, which has 13 of the MAX 8 variants in its 75-strong fleet.
"It has flown hundreds of thousands of hours globally and some of the world's largest airlines are flying this aircraft," it said in a statement.
Boeing has described the MAX series as its fastest-selling family of planes, with more than 5,000 orders placed to date from about 100 customers.
But not since the 1970s -- when the McDonnell Douglas DC-10 suffered successive fatal incidents -- has a new model been involved in two deadly accidents in such a short period.
The weekend crash sent Boeing shares nosediving as much as 12 percent on Monday, wiping billions of dollars off the market value of the company.
"I think the impact for the industry is significant," said Gerry Soejatman, a Jakarta-based aviation analyst.
"We have a new type of aircraft -- that type of aircraft has only been in service for two years -- and... we have two accidents with seemingly similar circumstances."