At least 17 people were killed on Sunday in attacks on two churches in Garissa, a town in eastern Kenya, police said.
The attacks in the normally quiet town are the latest in a series of incidents that have rocked Kenya since the government sent troops into southern Somalia last October to hunt down al-Shabab fighters who are said to have links to al-Qaeda.
Garissa serves as a military base for operations against the hardline Islamist fighters, who are attempting to overthrow the weak federal government in Mogadishu.
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 apart, at around 10:15am.
"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.
In March and April, Christian worshippers were targeted in grenade blasts that left two people dead.
The Vatican described Sunday's attacks as "horrible and very worrying".
Garissa is not far from the Dadaab refugee camp, where a Norwegian aid delegation was attacked on Saturday and four of its members taken hostage in their own car, which the kidnappers drove towards the Somali border.