NAIROBI, Kenya  — An explosion ripped through a building full of small shops in downtown Nairobi on Monday, wounding at least 16 people, the police commissioner said.

He could not immediately say what caused the early morning blast that sent smoke billowing out of the building and over the city. Items for sale in the shops — like shoes and clothes — were scattered on the ground.

People with bloody wounds received medical care, as authorities tried to usher hundreds of people in the street away from the scene. Security blocked off areas around the building with yellow tape.

The force of the explosion ripped apart the one-story building’s aluminum roof, but a high-rise building with a glass exterior right next to the blast did not appear to sustain major damage.

Police Commissioner Mathew Iteere said at least 16 people were wounded.

Another high-ranking police official said there were no obvious signs that the blast was caused by a terrorist’s bomb. No ball bearings or nails — lethal shrapnel packed into bombs — were found, and officials were investigating the possibility that a faulty electrical line caused the explosion. The official said he could not be quoted by name.

“Let me not speculate this is a terrorist attack. It could be a wire fault,” said another official Orwa Ojode, assistance minister for internal security.

Al-Shabab militants from neighboring Somalia have long threatened to carry out substantial attacks in Kenya following Kenya’s decision last October to send troops into Somalia to pursue al-Shabab militants.

Kenya has suffered a series of grenade attacks in recent months, but Monday’s blast appeared to have been caused by something larger than a grenade.