They were arrested from a prominent private hospital in southeast Delhi around 9 PM, a police officer said.
The police were tipped off about the gang's presence in the hospital, the officer said.
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The arrested are three middlemen, who are believed to have sold at least four kidneys so far in Delhi, and three potential donors, including two women, who were picked up from a village in north India, he said.
A case has been registered at Sarita Vihar police station and the accused are being interrogated to find out the gang's reach.