FBI agents went to the East African country after its government asked for the United States to help probe what happened aboard Daallo Airlines Flight 3159 soon after it set off from Mogadishu's airport on Tuesday, Somalian Prime Minister spokesman Abdisalam Aato told CNN.
"This was a sophisticated attack ... so we reached out to our international partners," Aato said.
U.S. sources familiar with the investigation confirmed that the FBI is assisting Somali authorities.
Transport Minister Jama Jangali told reporters Saturday it was terrorism, not "technical difficulties," that led to an explosion that ripped a hole about the size of a small door in the plane.
This blast -- which happened 12,000 to 14,000 feet above the ground -- killed one person and injured two others. But it failed to bring down the Airbus A321-111 plane, which the pilot managed to turn around and land safely in Mogadishu.
Somali officials on Friday identified the man sucked out of the airliner -- and the lone fatality -- as Abdullahi Abdisalam Borleh, an elderly Somali national.
Investigators suspect he carried a laptop computer with a bomb concealed onto the plane, according to a source familiar with the investigation.
The source said Borleh apparently knew precisely where to sit and how to place the device to maximize damage. The source said, given the placement, the blast likely would have set off a catastrophic secondary explosion in the fuel tank had the aircraft reached cruising altitude.
The bomb contained a military grade of the explosive TNT, according to the source, citing an initial analysis of residue recovered from the aircraft.
Investigators believe the attack was orchestrated by the al Qaeda affiliate Al Shabaab, although they are not certain that Borleh was a direct member of the group, according to the source. No group immediately took responsibility for the act.
, which has been linked to al Qaeda though it has factions that have declared loyalty to ISIS
, has been behind some of the worst violence in recent years in and around Somalia
Some of it targeted tourists, such as last month's deadly attack on a beachside restaurant-hotel complex in Mogadishu. Young people also have been targets, as shown in the massacre at Kenya's Garissa University College. The general public also hasn't escaped the group's violence, as evidenced in a 2013 assault on an upscale mall in Nairobi.