Officials in Kenya say at least 28 people were injured Sunday when an explosion went off in downtown Nairobi and set a gas station on fire.

Witnesses say the blast went off around 11 a.m. local time near Nairobi's Kirinyaga Road. The injured were taken to a local hospital, where several were being treated for serious burns.

Authorities have not ruled whether the explosion was accidential or set on purpose.

Kenya has experienced bombings in the past, most recently in December on a bus that was set to travel to the Ugandan capital, Kampala. At least two people died in that attack.

The Somali militant group al-Shabab has repeatedly threatened to attack Kenya because of its support for the U.N.-backed Somali government.