Police fire tear gas to stop attacks on Somalis after a deadly bombing over the weekend that killed at least nine people.
Ethnic Somalis, some armed with machetes, hurled rocks at their attackers, who responded with sling shots and stones. Paramilitary police fired volleys of teargas as they tried to prise the battling factions apart.
"We are trying to create a buffer zone so that people cannot cross over," Nairobi regional police commander Moses Ombati told reporters, pointing to a road that he said formed a rough boundary between the two communities.
"These people are neighbours and business partners who need each other, so I don't think it will last long," he said.
Authorities have blamed Somali militants and their sympathizers for grenade and gun attacks in Kenya since Nairobi sent soldiers into neighboring Somalia last year to drive out al-Shabaab rebels, an Islamist group linked to al Qaeda.
Attacks have intensified since Kenyan and African Union forces launched an offensive seven weeks ago against al Shabaab's last major urban stronghold, the Somali port of Kismayu, forcing the rebels to flee.
Two Kenyan soldiers were shot dead in the eastern town of Garissa, which is a rear base for Kenya troops fighting in Somalia as part of the regional African Union force.