Police in Kenya have fired bullets into the air and tear gas into the streets to stop two groups from clashing one day after an improvised explosive device ripped through a bus and killed seven people.

Alfred Mutua, a witness to Monday's clashes in downtown Nairobi, said people are angry at ethnic Somalis, whom many Kenyans broadly blame for a series of grenade and explosive device attacks in Kenya over the last year. Mutua said others are trying to take advantage of the chaos by looting shops.

The Somali militant group al-Shabab has vowed large-scale attacks in Nairobi after Kenya sent military forces into Somalia last year. A series of explosive attacks over the last year have killed and wounded dozens, raising ethnic tensions.