One person was arrested and more than 100 sachets of heroin seized by police in Nairobi's Mathare slums.
The police said they were yet to establish the source of the narcotics, as slums emerge as the biggest market.
Detectives said a sachet of the addictive drug costs up to Sh500.
The 30-year-old suspect arrested during a raid at Kampala Ndogo is said to be the main supplier of the drug.
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He was found hawking the drugs, making police to conclude that there was steady supply in the area.
"What we are yet to establish is how these drugs find their way into the slums and the barons behind it because the suspect we have arrested is just a seller," said Nairobi head of Directorate of Criminal Investigations (DCI) Bernard Nyakwaka.
Made seizures
Police have in the past made such seizures but failed to make follow-ups on the source, which has made it difficult to break the chain of supply.
The police suspect those behind the supply of the narcotics are powerful individuals. They said most of those they had been arresting and arraigning for selling such drugs were not the real people behind the trade.
DCI boss George Kinoti said he had ordered detectives to always make follow-ups after such seizures.
"Be it drugs, contraband goods, money laundering or any other crime, we must deal with the entire chain," said Mr Kinoti.
Drug abuse in Nairobi, especially in slums, has become rampant. The situation has been compounded by the fact that the narcotics are easily available, according to police.
“If you walk through Kampala Ndogo and Kosovo in Mathare, you will not believe it. People are dying for abusing drugs. Yet we don’t know how they get there and those behind the trade,” an anti-drugs campaigner said yesterday.