Four persons, including a woman, were arrested with 6.5 kg of trinitrotoluene in Mumbai on Saturday, and police said they were trying to ascertain whether the explosive material was obtained from defence establishments in a cantonment near Nashik.
The arrests were made in north-west Mumbai by a team of officials from D N Nagar police station, who laid a trap for persons who were reportedly trying to sell the TNT.
A constable was sent as a dummy customer and this led to the arrest of Sakhubai Gaikwad and Gautam Telore with 900 grams of TNT, Additional Commissioner of Police (West Region) Bipin Bihari said.
Their interrogation led to the arrest of two more men -- Harishchandra Telore and Sanjay Pawar -- and five kg of TNT was seized from them.
An official who is part of the probe said TNT is a banned highly explosive substance that is stored only by military establishments manufacturing and assembling ordnance for heavy artillery.
"We are investigating if the material could have been procured from Deolali cantonment near Nashik as all of the four arrested persons hail from areas in the vicinity of the cantonment," he said.
The persons hail from villages close to Deolali in Nashik, Bihari said.
They were booked under the Explosives Act and produced before a local court, which remanded them to police custody till January 29.
Police are looking for a fifth person who allegedly supplied the explosives to the four arrested men.
An investigating officer said Gaikwad had contacts with criminals in Mumbai and also helped some accused in murder cases to get bail. She used to make frequent visits to Mumbai, he said.
This is the first time that such a large quantity of TNT, used in making bombs and other explosives, has been seized from any person in the city, Bihari said.