At least 17 people have been killed in attacks on two churches in Kenya's eastern town of Garissa, police said.
Garissa is serving as a military base for operations against the Islamist fighters.
Witnesses said bodies lay scattered in the blood-spattered churches as scores of wounded were rushed to hospital.
"It is a horrible sight to see," said Hussein Abdi, a resident of Garissa.
Regional police chief Philip Ndolo said a total of seven attackers hurled grenades inside the Catholic Church and the African Inland Church before opening fire with guns.
Two police officers were among the dead.
The assailants struck the churches, which are 3km (two miles) apart, at around 10.15am (0715 GMT).
"The goons were clad in balaclavas and hurled the grenades at the Catholic Church and the [African Inland Independent Church] in the town," Ndolo told the Reuters news agency.
Christian worshippers have been previously targeted in grenade blasts that left two people dead in March and April.
The Vatican described Sunday's attacks as a "horrible and very worrying" act.
"The bloody attacks in Kenya in the town of Garissa against two churches, including a Catholic cathedral, during Sunday prayers, are a horrible and very worrying fact," Federico Lombardi, the spokesman, told Vatican Radio.
Garissa is not far from the Dadaab refugee camp, where a Norwegian aid delegation was attacked yesterday and four of its members taken hostage in their own car, which the kidnappers drove towards the Somali border.
Recent attacks in Kenya are believed to be the work of groups sympathetic to al-Shabab, the Islamist group fighting to overthrow the Somali government, Al Jazeera's Nazanine Moshiri said. By A Web design Company
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