An unfurnished one-bedroom house in Dombivli is believed to have been one of the main 'military' production units of the banned Communist Party of India (Maoists).
The Maharashtra Anti-Terrorist Squad raided the premises rented by Asimkumar Bhattacharya, 63, and arrested him and three other CPI (Maoist) members.
Bhattacharya was allegedly running an engineering unit in the house, making parts and accessories for rocket launchers.
The other three arrested CPI (Maoist) members, belonging to Korchi Dalam in Gadchiroli, have been identified as Dinesh Wankhede, 30, Suman Gawde, 40, and Paru Patel, 40.
Officials said the house did not have any amenities except for a 12-inch television set. ATS raided the house based on an intelligence input from the Andhra Pradesh (AP) police's counter-intelligence wing.
The ATS recovered Rs23.07 lakh in cash, a laptop, a printer and a pen drive. They also recovered 13 aluminum pressure plates, a rocket-shaped hollow aluminium pipe and eight iron pipes.
Key documents along with driving licences and rent receipts have also been recovered, ATS officials said.
ATS chief Rakesh Maria confirmed the arrests and said the ATS have handed the four to the Gadchiroli police for further investigation.
The arrests, part of the country-wide crackdown on the 'military' supply chain of CPI (Maoists), is also linked to the arrest of top Maoist member Sadnala Ramakrishna, alias RK, and four others in West Bengal.
Ramakrishna, who is part of the Central Military Committee and secretary of the Andhra Pradesh-Orissa Border Special Zonal Committee, had recently taken over slain Maoist Kishenji's position in West Bengal. AP police sources said that the Mumbai centre provided weapon parts for the Dandakaranya Special Zonal Committee, which controls regions of Chattisgarh, Jharkhand and AP.
Bhattacharya, who originally hails from West Bengal and spent the early years of his life in AP, is suspected to have close links with Ramakrishna, ATS sources said.
Bhattacharya claims to be a mechanical draughtsman and has been staying in Dombivli for the last 30 years in rented accommodation.
Preliminary interrogation has revealed that he supplied these parts to a person named 'Kasturi', but claimed he did not know his whereabouts or where he came from, said ATS sources.
The Dombivli house was also used as a medical shelter for the naxals, and one of the Maoists, Paru Patel, was undergoing treatment there.
The four were also members of the central technical committee (CTC) of the naxals.
"They have been hiding in Dombivli since October 2011," said an ATS source.