Mungiki, Taliban or whatever they will call themselves tomorrow, we are determined to wipe them out and we are sure we will wipe them out,” Mr Michuki, a former colonial administrator, told a news conference.
Police at a station in Nairobi paraded six men it had arrested and urged the public to help identify more suspects.
“We don't want to concentrate on big words like Mungiki. We want the public to come up with names of individuals among themselves who they know are involved in illegal activities,” police spokesman Eric Kiraithe said.
A 50-year-old victim's headless body was dumped at the gate of a chief - a junior government official.
Another was perched atop a telephone pole about a kilometre away, and another was found after villagers heard two dogs fighting over it.
In Kiambu, which borders Nairobi, one head was left at a bus stop in the centre of the main town, local media said.