Thirty-three criminal groups have been proscribed and the public warned against dealing with them in any way.
Harsh penalties, including life imprisonment and hefty fines of up to Sh1 million will be imposed on those who do.
The groups are declared illegal in a gazette notice by Internal Security minister Prof George Saitoti. They include the Mungiki sect and the Somali-based Al-Shabaab.
The notice is in line with The Prevention of Organised Crimes Act, which came into force last month.
The list includes some old groups — proscribed in a similar manner in 2000 — as well as new ones in Nairobi, Western, Coast and Nyanza provinces.
The ministry’s permanent secretary Francis Kimemia cautioned that the new law criminalises even non-members who allow the groups to use their properties in carrying out their activities. “Abetting and aiding in crime will lead to imprisonment for a term not exceeding 14 years or a fine not exceeding Sh1 million or both,” reads the Act.
“While the justice system will implement the law without fear or favour, the public is cautioned to note and avoid the criminal groups,” said Mr Kimemia.
In the past, criminal groups have engaged in macabre killings and kidnappings, while imposing illegal levies and administering oaths. The Act stipulates life in jail without a fine if a person dies as a result of criminal gang activities. Those charged with administering oaths would attract a similar sentence.
In the past, witnesses have failed to appear to testify against criminals in court for fear of retaliatory attacks.
But now those who threaten witnesses are liable to a term not exceeding 10 years and a fine of Sh500,000. The law also empowers the government to seize property and money acquired through criminal activities. Since the law came into force, there has been an intensified crackdown on Mungiki sect members and hundreds of them have been charged in court.
Mr Kimemia said the Counter-Trafficking in Persons Act would come into force in December to complement the fight against organised crime.