A grenade explosion killed seven people and wounded another 24 on Sunday in a predominantly Somali neighborhood of Nairobi, a Kenya Red Cross official said.
The grenade was tossed onto a minibus, known as a matatu, full of passengers riding through the Eastleigh section, according to local media reports.
No group has claimed responsibility for this attack.
Such attacks have escalated since Kenyan forces invaded neighboring Somalia last year to battle the Islamist militant group Al-Shabaab, blaming it for kidnappings of foreigners in the nation.
A grenade thrown into a Kenyan church two weeks ago turned a prayer service into carnage, killing one worshipper and wounding 13 others.
Witnesses said members of Al-Shabaab were involved, said Nelly Muluka, spokeswoman for the Kenya Red Cross.
Seven weeks ago, one child died and several others were hurt in a grenade attack on a children's Sunday school class in Kenya, the Kenya Red Cross said.
Kenyan forces are engaged in a fight in SomalIa to debilitate Al-Shabaab. The group once held large territories in Somalia, but has lost significant ground in the past year, including its southern base of Kismayo, which Kenyan forces took in late September.