A explosion rocked a commercial plane after it set off above East Africa on Tuesday, injuring two people before the pilot landed safely, a passenger said.

Pictures from the ground showed a hole in one side of the Daallo Airlines plane, just above its wing and slightly smaller than one of its doors.

Initial tests of the damage on Flight D3159 came back positive for explosive residue, a source with knowledge of the investigation told CNN.

A spokesman for Somalia's Prime Minister didn't immediately indicate a bomb had gone off mid-flight, echoing a Daallo Airlines worker in saying "the incident is under investigation."

"There is a lot of conflicting information," said the Prime Minister's spokesman, Abdisalam Aato.

An airport official estimated the Daallo plane was between 12,000 and 14,000 feet high when the blast occurred not long after it took off from Mogadishu International Airport.

The pilot then flew the aircraft, which had originated in Jeddah on Saudi Arabia's coast, back to the Somali capital.

If this was a bomb, no group immediately took responsibility.

Al-Shabaab 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. And the general public hasn't escaped the group's violence, as evidenced in a 2013 assault on an upscale mall in Nairobi.

Yet this Islamist extremist group has recently gotten competition from ISIS, with a high-ranking Al-Shabaab member and spiritual leader pledging allegiance to the rival group last fall.

Flights in and out of Mogadishu International Airport were suspended briefly Tuesday because of the Daallo Airlines incident.

That airport is home to offices of the United Nations, African Union and many diplomatic missions, including those of the United States and European Union.

Somalia jet explosion: 2 injured, hole left in plane - CNN.com