The US Federal Aviation Administration has told airlines that the Boeing 737 Max 8 model is capable of flying after two fatal crashes within six months.
An Ethiopian Airlines plane en route from Addis Ababa to Nairobi crashed six minutes after launch on Sunday, killing all 157 people on board.
The incident followed the accident of Lion Air 737 Max 8 in October, in which 189 people died.
Some members of the aviation community have demanded that the aircraft be grounded until fully inspected.
But late on Monday, the Federal Aviation Administration (FAA) issued a continuing airworthiness notification stating that the aircraft could fly safely.
China, Indonesia and Ethiopia ordered their airlines to ground the jet on Monday. Aerolineas from Argentina, Mexicos Aeromexico and Brazil's Gol have also suspended flights on the plane.
The civil aviation authority of Singapore said on Tuesday that it had "temporarily stopped operating all variants of the Boeing 737 Max in and out of Singapore".
The suspension will be effective from 14:00 local time (06:00 GMT).
Other airlines continued the 737 Max 8 after Boeing said it was safe.
Boeing shares fell 12.9% on Monday after the crash.
What did US authorities say?
US Secretary of Transportation Elaine Chao said the FAA would "act promptly and appropriately" if a defect were found on the plane.
FAA chief Dan Elwell said the notification "informs the international community where we are and gives (an) response to the entire community".
Paul Hudson, President of FlyersRights.org and a member of FAA's Advisory Committee on Aviation Rules, called for the plane to land.
"The FAA's attitude is cautious and jeopardizes the life and reputation of the American aviation industry in safety," Hudson said in a statement Monday.
What do we know about the crash?
The plane landed near the town of Bishoftu, 60 km southeast of the capital. The cause of the disaster is not clear, but the pilot had reported difficulties and asked to return to Addis Ababa.
The investigators have found the cockpit voice recorder and digital flight recorder, but it will take some time for the results to be published.
It was said that the visibility is good, but the air traffic monitors flightradar24 reported that the vertical speed of the aircraft was unstable after takeoff.
The pilot was named as Senior Capt Yared GetachewEthiopian Airlines said it had a "commendable performance" over more than 8,000 hours in the air.
Several witnesses who worked on the farmland below the trajectory of the aircraft told the Reuters news agency that they heard loud rattling noises from the plane.
"When it floated, the fire followed his tail, then tried to lift his nose," said one witness, Gadisa Benti. "When it crossed our house, its nose was pointing down and its tail was raised, its nose went straight to the ground and then exploded."
What do we know about the plane?
Introduced in 2017, the Max 8 is the latest version of the 737 series. By the end of January, Boeing 350 had delivered the model of 5,011 orders.
The crashed aircraft was among six of the 30 aircraft that Ethiopian Airlines had ordered as part of the expansion. It underwent a "strict first maintenance". On February 4, the airline announced.
Boeing said it was "deeply saddened" through the crash and sent a team to provide technical support.
After the plane crash of Lion Air last October in Indonesia, the investigators said the pilots had apparently had to contend with an automated system that should not bring the aircraft to a halt, a new function of the aircraft.
The anti-stall system forced the nose of the aircraft repeatedly down despite the pilots' efforts to correct this problem. The Lion Air plane was also new and the accident occurred shortly after takeoff.
Following this accident, Boeing sent an emergency notification to the airlines, warning them of a problem with the anti-stall system.
Boeing is expected to release a software patch for the system to solve the problem, Reuters reports.
It is not yet clear if the anti-stall system was the cause of the crash on Sunday. Aviation experts say that other technical problems or human errors can not be ruled out.
Who were the victims?
The flight included people of more than 30 nationalities, including 32 Kenyans, 18 Canadians, nine Ethiopians and nine Britons (two of whom were dual nationals with non-British passports).
Among the Canadians was a family of six, originally from India. Kosha Vaidya (37) and her husband Prerit Dixit (45) brought their 14-year-old daughter Ashka and 13-year-old daughter Anushka along with their parents, Pannagesh Vaidya (73) and Hansini, to Nairobi, where Kosha was born Vaidya, 67 ,
On board were also eight Italians, eight Chinese, eight Americans, seven French, six Egyptians, five Germans, four Indians and four people from Slovakia.
At least 21 passengers were connected to the UN and traveled to a meeting of their environmental assembly in Nairobi.
"It's one of the biggest disasters we've had in years," said Michael Moller, director-general of the UN Office in Geneva, Monday.
What happens next?
The investigation will be conducted by Ethiopian authorities in consultation with Boeing expert teams and the US National Transportation Safety Board.
Ethiopian Airlines said it has grounded all 737 Max 8 aircraft "until further notice" as "additional security measure". The airline's first flight to Kenya since the crash landed at 10:25 am local time on Monday and another aircraft model was deployed.