Four people including two Kenyan women were on Sunday night arrested with four kilogrammes of heroin valued at Sh10 million in Kitsuru area, Nairobi.
The other two include two Nigerians who police say have been supplying the drugs to the Kenyan women who in turn sold them to university students in the city.
They were arrested following a police operation by officers from Anti-Narcotics Unit and those from Special Crimes Prevention Unit (SCPU).
Head of SCPU Said Kiprotich said they were tipped that there were up to 40 kilogrammes of the drug in the house but they only found Â four kilogrammes.
â€œIt seems they had sold or supplied out the rest but we are interrogating the suspects to know more on where the rest could be,â€ said Kiprotich.
Police say the four were expected in court Monday to face charges of trafficking in narcotics.
The Nigerians are also said to be in the country illegally. They had chosen the house in the leafy suburb to avoid suspicion, police say.
The arrest came three days after detectives at the Jomo Kenyatta International Airport intercepted 5.436 kilos of heroin valued at Sh14 million and arrested a Tanzanian woman aged 25, who was attempting to smuggle it into Kenya.
Kenya Revenue Authority (KRA) Senior Deputy Communication Commissioner Kennedy Onyonyi said the drugs were wrapped in a black paper to avoid detection and hidden in a suitcase.
The woman was headed for Budapest through Brussels when she was arrested on Wednesday.
Police believe most of the drugs in circulation in the country originate Tanzania and the traffickers use the airport or roads in bringing them.
Onyonyi added that further investigations to establish the source of the drugs are going on between the JKIA, KRA Enforcement Surveillance and Targeting Team and the JKIA Anti-Narcotics officers.
Officials at the airport have been on alert and have upped their surveillance as part of efforts to curb trafficking.-Standard