Indian intelligence agencies have uncovered at least 800 terrorist cells in the country operating with "external support," and are now looking for the brains behind them within India, National Security Adviser M K Narayanan has said.

"We are concerned that there is a great deal of external inspiration and support, we are also concerned and are looking at a mastermind within the country," Narayanan told Singapore's Straits Times in an interview, when asked about investigations into the blasts that rocked Bengaluru and Ahmedabad on consecutive days.

Narayanan said intelligence agents had "disrupted" several modules, some of which are "not entirely foreign".

"Clearly, there is some kind of organisation. We have to find out if that organisation is localised or there is an external group or module operating," he said without elaborating.

He also expressed concern over the bombing of hospitals by terror outfits in Ahmedabad [Images] -- the first instance of a hospital being targeted by terrorists in India. "Copycat systems are coming up," he said.

"Like putting bombs in vehicles near hospitals soon after blasts, knowing that large congregations will be there and impact will be much greater," Narayanan said.