Kenyan police have arrested two people, one of them a pastor, found with materials capable of making an explosive device, the police spokesman said.
Eric Kiraithe said they seized the two in Nairobi on Saturday afternoon after being tipped off.
"Police officers ... intercepted two persons in possession of materials capable of making (an) improvised explosive device," he said in a statement late on Saturday.
"Pastor John Kamau of Mission Church ... and an accomplice, Samuel Chege Gitau, were arrested and a substance believed to be prilled ammonium nitrate, a detonator and a safety fuse were also recovered from them," he said. Prills are small beads.
Kiraithe said they were investigating the duo's motives and establishing if they had other accomplices.
In mid-June, grenade attacks at a rally organised by church leaders opposed to a new constitution killed at least six people and injured dozens.
Kenyans are due to vote on the new charter at a referendum on August 4. The new constitution will replace one that has been in use since independence from British colonial rule in 1963.
"Police are taking all possible measures to ensure law and order is observed during the referendum campaigns and on the voting day," Kiraithe said.
Almost two-thirds of Kenyans intend to vote for the new constitution next month although just as many say it need some amendments, an independent poll released on Friday showed.
Saturday's arrests were made barely a week after twin bomb attacks in Kampala killed 73.
Somalia's al Shabaab insurgents linked to al Qaeda said they had carried out the attacks, on a crowded restaurant and a rugby club in the Ugandan capital while fans watched the World Cup final on television.