One child has been killed and three seriously hurt, police say, in a grenade attack on a church's Sunday school in the Kenya capital, Nairobi.
The attacker targeted St Polycarp's church on Juja Road.
A police spokesman blamed sympathisers of Somalia's al-Shabab Islamist militant group, angry over Kenya's role in the UN-backed intervention force.
A mob later rounded on Somalis living near the church with sticks and stones in a suspected revenge attack.
Police chief Moses Nyakwama told the BBC's Focus on Africa programme that 13 people had been injured in the revenge attack, in the suburb of Eastleigh.
Separately, two police officers were killed in an ambush in the town of Garissa, near the border with Somalia.
In July, 15 people were killed in raids on churches in Garissa, and there was speculation that al-Shabab or its sympathisers were responsible.
'Running for their lives'
Reports suggested a number of those hurt at the church were injured in a stampede after the attack.
A police spokesman, Charles Owino, told Reuters news agency: "We suspect this blast might have been carried out by sympathisers of al-Shabab.
"These are the kicks of a dying horse since, of late, Kenyan police have arrested several suspects in connection with grenades."
The authorities said three children were seriously hurt in the attack, and a number of others suffered lighter injuries.
The Red Cross had earlier said six children were critically wounded.
Irene Wambui, who was in the church at the time of the attack, said: "We were just worshipping God in church when suddenly we heard an explosion and people started running for their lives.
"We came to realise that the explosion had injured some kids who were taken to hospital and unfortunately one succumbed."
Senior Nairobi police officer Moses Ombati appealed for calm after youths reportedly attacked the nearby Alamin mosque.
Nairobi and the port city of Mombasa have suffered a series of grenade attacks since Kenya sent troops into Somalia last October.
The attacks in Mombasa escalated after radical Islamist preacher Aboud Rogo Mohammed was killed in a drive-by shooting in August.