In the port city of Mombasa, attackers on a motorbike threw a homemade bomb into a church service, wounding seven, while in Nairobi, a grenade was thrown in the largely ethnic Somali district of Eastleigh, police said.
The attacks are the latest in a string of grenade blasts or shootings to have hit Kenya, although it was not immediately clear if the two attacks were connected.
In Mombasa, coastal police chief Aggrey Adoli said that police were searching for the attackers.
The blast was believed to be caused by an improvised petrol bomb.
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In Nairobi, the capital's police chief Benson Kibue said "a grenade was thrown at a crowd within the Majengo area of Eastleigh, and three people have been injured."
Kenyan police have previously blamed similar grenade attacks on supporters or members of Somalia's Al-Qaeda-linked Shebab insurgents.
Kenyan troops invaded southern Somalia in 2011 to attack Shebab bases, and have now joined an African Union force to battle the extremists there.
Kenya's invasion however sparked an angry reaction and warnings of revenge from the Islamists.