The two accused, Darbara Singh alias Billa (48) and his nephew Ajay alias Sandeep Singh (19), were arrested from Uttam Nagar in west Delhi with the police claiming to have seized the heroin, worth Rs 16 crore in international market, from them.
"On May 1, an information was received that the duo would receive huge consignments of heroin. A trap was laid and the accused were nabbed while they were in a car," said Sanjeev Kumar Yadav, DCP (Special Cell).
Three kilograms of heroin was seized from Darbara Singh, while one from Ajay. An Alto car with a Punjab registration number and three mobile phones have also been seized, he said.
He said the Special Cell sleuths were working for the last three-four months on tip-off about an international drug cartel being active in Uttar Pradesh, Delhi, Punjab and Haryana.
The heroin, that is supplied to these places, is smuggled from Afghanistan and Pakistan, DCP Yadav said.
The arrested accused were supplied heroin by a man residing in Uttam Nagar.
It emerged that carriers from Afghanistan and Pakistan used to bring heroin in their stomachs by having capsules of heroin, said the officer.
They would then hand over the heroin to suppliers in Delhi which was further supplied to the drug dealers in UP, Punjab and Haryana.
The suppliers also used to send consignments of heroin to other countries, including England, France, Canada and South Africa, through courier companies and other modes, he added.
During interrogation, it was revealed that Singh is an associate of one Buta Singh, a Punjab-based drug supplier who is currently lodged in Nabha jail.
Police said Singh was convicted in three cases of the Narcotic Drugs and Psychotropic Substances Act in Punjab and awarded 32 years imprisonment with a fine of Rs 3 lakh.
He was granted parole in 2015 for some days when he absconded.
He went underground and restarted the illegal trade of drug trafficking. For more than one-and-a-half years, he has been receiving supply of heroin from some persons and their woman associate in Delhi, police said.
His wife Sarabjeet Kaur is also involved in at least 10 cases registered against her under the NDPS Act. She is also convicted in two of these cases.
She is facing trial in other cases and is currently lodged in Ludhiana Jail.
Ajay gets Rs 10,000 per trip to Delhi and has been coming here along with Singh for the last six months, they said.