Two Kenyan police officers have been shot dead in the northern town of Garissa, near the border with Somalia, police said.
The shooting on Sunday came hours after a nine-year-old boy was killed in the capital Nairobi by a grenade attack on a church by suspected sympathisers of Somalia's al-Shabab group and days after Kenyan troops led an offensive against the fighters in their last stronghold of Kismayo in Somalia.
Herman Ndiema, Garissa's deputy police chief, told the Reuters news agency the two officers were killed as they walked to a technical college they had been assigned to guard.
Their killers drove up to them in a taxi, shot them dead, and then jumped out to steal their guns, he said.
"We suspect sympathisers of the al Shabaab militant group were behind the attack and we have sealed all exit routes to nab them," Ndiema said.
The stolen guns, G3 rifles, were later recovered a short distance from the scene of the attack, a regional administrator said.
Security was stepped up in the town with members of the security forces patrolling it by car.
Kenya has been hit by a series of grenade and gun attacks since it sent troops into Somalia last October in pursuit of the al-Shabab group whom it blamed for kidnapping its security personnel and Western tourists.
The killing of the police officers and the attack on the church came days after Kenyan troops launched a surprise offensive on the southern Somali port of Kismayo, al-Shabab's last stronghold, forcing the rebels to flee.
Al Jazeera's Mohammed Adow, reporting from Nairobi, said "there is an increasing nervousness about these attacks and people are afraid [the attacks] will become bolder".
"There are also fears that since places of worship are being targeted, such events might stir religious hostilities ...leaders are appealing to people to keep calm," our correspondent said.
Police had warned there was a heightened risk of attacks soon after the Kenyan army led an assault against the
rebels in Kismayo under cover of darkness on Thursday, local newspapers said on Sunday.
'Kicks of a dying horse'
Earlier in the day, a nine-year-old boy was killed and three other children wounded when a hand grenade was thrown into a Sunday school session in a church in the capital Nairobi, police and medical staff said.
Police said attackers threw the grenade into the Sunday school service in St Polycarp's church on Nairobi's Juja Road.
The grenade exploded, spraying the children with shrapnel and fatally injuring the boy.
"We suspect this blast might have been carried out by sympathisers of al Shabab," Charles Owino, a police
"These are the kicks of a dying horse since, of late, Kenyan police have arrested several suspects in connection with
grenades," he said.
Police also said they had found bomb making equipment in a bag on a bus carrying passengers from Garissa to Nairobi on Friday.
All 60 passengers on board had been detained after no one admitted ownership of the bag, the papers said.
Masked assailants launched simultaneous gun and grenade raids on two churches in Garissa in July, killing at least 17