At least four people haved been killed and 36 others wounded in a grenade attack on a bus in the Kenyan capital Nairobi, Kenyan officials said.

"So far I can confirm that four people have died in the explosion," Benson Kibui, Nairobi county police commander, told Reuters, without giving details. Another police officer described it as a grenade attack.

The minibus was travelling on the Juja road in the Pangani area of Nairobi's Somali-dominated Eastleigh neighbourhood when the blast happened in the early evening on Saturday.

"The bus is shredded into pieces. There's a body next to the bus as well. A lot of people have been taken to nearby hospitals," Mohammed Dahir, a journalist at the scene told Al Jazeera. 

On Friday twin explosions in the northeastern town of Wajir killed one person and injured at least three others.

This is the fourth attack in the 50th anniversary week of Kenya's independence. No one has claimed responsibility for the attacks which have left 13 people dead since Tuesday.

Kenya has suffered a string of deadly attacks in its capital Nairobi, the port city of Mombasa as well as the northeastern garrison town of Garissa since its  intervention in Somalia to fight the al-Shabab armed group.

Source: Al Jazeera and agencies