The four were arrested in the wee hours and produced before a magistrate, who sent them to 15 days judicial custody.
Acting on specific intelligence inputs, DRI sleuths intercepted a car in which the four persons were carrying 4.25 kg gold and 10 kg diamonds, which were smuggled into the country via Nepal border.
They were reaching the city by road from Jaipur.
A DRI official said that a lookout notice was issued by Intelligence Bureau (IB) officials and Customs department against the mastermind of the racket, Pradip Jagada (45), a resident of Veraval.
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Pradip Jagada's wife Bharti (40), son Dharmendra Jagada (21) and an assistant from their village, Vicky, were arrested along with him, the official said.
DRI officials said that a large gang seems to be at work and they are investigating into the direct and indirect support for these four persons.
The diamonds were said to be blood (conflict) diamonds without Kimberley Process Certification Scheme (KPCS). Also the value of the consignment could be higher than estimated, they said.