(CNN) -- All 157 people aboard an Ethiopian Airlines flight that crashed soon after taking off Sunday morning from Addis Ababa have been killed, the airline said Sunday.
The plane, en route to Nairobi, Kenya, lost contact at 8:44 a.m. local time, six minutes after taking off from Bole International Airport in the Ethiopian capital.
Flight ET302 went down near Bishoftu, southeast of Addis Ababa.
An airline spokesman told CNN the victims were of 35 different nationalities.
Thirty-two Kenyans, 18 Canadians, nine Ethiopians, eight Americans, eight Italians and eight Chinese nationals were among the passengers. Seven French and seven UK nationals were also on board, the spokesman said.
Also among the dead are several UN staff, according to an official, who said it's believed that some of the staff members were freelance interpreters. The specifics are unclear because UN staff members don't always travel with their UN passports.
Though it's unclear why UN employees were on the plane, the UN Environment Assembly is scheduled to begin Monday in Nairobi.
UN Secretary-General Antonio Guterres said in a statement that he "conveys his heartfelt sympathies and solidarity to the victims' families and loved ones, including those of United Nations staff members, as well as sincere condolences to the government and people of Ethiopia."
The US National Transportation Safety Board is sending a team to support the Ethiopian Accident Investigations Bureau's investigation, with assistance from technical advisers from the Federal Aviation Administration, Boeing and General Electric.
Ethiopian Airlines CEO Tewolde GebreMariam told reporters the pilot reported technical difficulties after takeoff and asked for clearance to return to Addis Ababa.
He was given clearance to turn back, GebreMariam said, citing the air traffic controllers' record.
The pilot was a senior Ethiopian Airlines pilot who had flown more than 8,000 hours. He had an "excellent flying record," GebreMariam said.
The CEO visited the crash site Sunday. He said the plane "is now right inside the ground" and it was not possible to identify whether it was an emergency landing or a crash. He said there was still smoke at the site when he visited.
"As it is a fresh incident, we have not been able to determine the cause. As I said, it is a brand new airplane with no technical remarks, flown by a senior pilot and there is no cause that we can attribute at this time."
"The routine maintenance check didn't reveal any problems," GebreMariam added.
Asked about the possibility of terrorism or sabotage, he said, "At this stage we cannot rule out anything."
The airline said a passenger information center and hotline "will be available shortly for family or friends of those who may have been on flight."
The Ethiopian government expressed its "deepest condolences to the families," the office of Prime Minister Abiy Ahmed tweeted.
Ethiopian Airlines has a reputation of being one of the best airlines in Africa. It has a good safety record and the newest fleet of planes on the continent, according to its website.
The Boeing 737 MAX 8 is the same type of plane as the Indonesian Lion Air jet that crashed soon after takeoff from Jakarta in 2018 -- killing 189 people, GebreMariam said, adding that only an investigation would yield conclusions.
Geoffrey Thomas, the editor in chief of Airline Ratings, told CNN that Sunday's crash had "significant differences" to the Lion Air crash. In the Lion Air flight, there were "wild fluctuations in air speed and ... we continued to get data from the plane all the way down to impact."
Sunday's crash, however, had "no fluctuations and all of the sudden transmission" ceased, he said. "That transmission ceasing indicates catastrophic failure in air."
The aerospace giant said in a press statement that it was "deeply saddened to learn of the passing of the passengers and crew." It added that a "Boeing technical team is prepared to provide technical assistance at the request and under the direction of the US National Transportation Safety Board."
The last major accident involving an Ethiopian Airlines passenger plane was in January 2010, when a flight from Beirut went down, killing 83 passengers and seven crew.
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