While their movement does not have the same intensity as in the neighbouring states, authorities say they cannot relax vigil as an estimated 240 extremists are known to be present in Gadchiroli alone, one of the two worst-affected districts.

However, the threat to urban centres could change the nature of the insurgency, they admit.

Intelligence sources suspect that some frontal organisations of Naxals operate in Thane’s tribal and backward taluks of Jawahar and Mokhada. These areas are densely forested and some of them are considered to be Communist strongholds.

The support for radicalism could not be termed as “full-fledged Naxal activity” and the movement is still in its “first stage”, Thane SP Naval Bajaj told The IndianExpress.

“There are so many frontal organisations which are working in the area. So, I have informed my officers to talk to people personally and remove the middlemen from the picture,” he said. “By this, we can understand the problems of the people. The problem is more a ‘socio-economic’ one at this point of time.”

While the urban parts of Thane are a part of the Mumbai Metropolitan region (MMR) and get funds for development, the rural areas are largely neglected and these differences are being exploited by some radical groups, another senior officer said.

Mumbai gets its water from dams in the district, most of them located in the tribal taluks, but residents of the tribal hamlets walk miles to get potable water.

The tribal taluks have also reported malnutrition deaths along with problems like unemployment and poverty. The threat could blow up if not handled now, officers warned.