The six contacted the responsible authorities and said that they were sent by a senior physician named Rezaul Karim to collect oxygen cylinders and deliver them to some hospitals in the capital.
The detainees also added that they had documents supporting their statement.
However, Abu Sayeed Khan Babu, the man in-charge of oxygen cylinders at the Rangpur hospital, immediately informed the police personnel on duty in the hospital checkpost about the situation.
Acting on that lead, a team of Kotwali police reached the area and detained the suspected oxygen cylinder smugglers following initial interrogation.
They were in custody of Kotwali police as of filing of this report.