The head of Ethiopian Airlines says he cannot rule out anything as the cause of Sunday's crash of a passenger jet moments after takeoff from Addis Ababa, killing all 157 on board.
"Ethiopian Airlines is one of the safest airlines in the world," Tewolde GebreMariam told reporters while visiting the crash site.
He stood inside the crater where the Boeing 737-MAX 8 went down with the ground littered with plane parts and body bags.
China has ordered Chinese airlines to ground all their Boeing 737-Max 8 jets.
The flight was on its way to Nairobi. Citizens from at least 35 countries were on the Boeing 737-MAX 8, including 19 United Nations workers.
"The secretary-general was deeply saddened at the tragic loss of lives in the airplane crash today near Addis Ababa," a spokesman for Antonio Guterres said.
"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 spokesman added.
U.S. State Department Deputy Spokesman Robert Palladino said in a statement late Sunday, "The U.S. Department of State extends our deepest condolences to the families and friends of those killed in the tragic crash of Ethiopia Airlines flight ET302. We can confirm that at least eight U.S. citizens were among the victims."
"We extend our heartfelt sympathies to the families and loved ones of the passengers and crew on board and stand ready to support the Ethiopian Airlines team," Boeing said in a statement late Sunday. "A Boeing technical team will be travelling to the crash site to provide technical assistance under the direction of the Ethiopia Accident Investigation Bureau and U.S. National Transportation Safety Board."
The Ethiopian Airlines jet went down in clear weather near the city of Bishoftu shortly after takeoff.
The Boeing 737-MAX 8 was a new jet, delivered to the airline in November, according to Planespotters, a civil aviation database.
Boeing issued a one-line statement Sunday, saying, "Boeing is aware of reports of an airplane accident and is closely monitoring the situation."
Flightradar24, which tracks planes in real-time, posted on Twitter that the "vertical speed" of the Ethiopian aircraft "was unstable after takeoff."
The Boeing 737-MAX 8 is the same model that took off in October from Jakarta and crashed into the Java Sea a few minutes later, killing all 189 people onboard a Lion Air flight.
Investigators with Indonesia's National Transport Safety Committee issued a preliminary report on that disaster in November.
The report was based on information from the flight data recorder, and said the plane's automatic safety system repeatedly pushed the plane's nose downward despite the pilots' desperate attempts to maintain control.
They believe the automated system that prevents the plane from stalling if it flies too high on Boeing's new version of its legendary passenger jet received faulty information from sensors on the fuselage.
The plane had a similar problem on a flight from the resort island of Bali to Jakarta the night before the fatal crash. The investigators said the plane was not airworthy and should have been grounded after that flight.
Boeing had planned to unveil its latest 777x widebody Wednesday in Seattle, but has cancelled the debut to instead focus on "supporting" Ethiopian Airlines, according to Reuters news agency.
Peter Clottey, Margaret Besheer contributed to this report.