"There are ample inputs suggesting that the Lalgarh operation of the ultras did not take all of a sudden. A slow build up was happening from much earlier. The West Bengal Naxal units are being assisted by the those from the neighbouring Jharkhand and Orissa also," sources said.

Pointing out that there was nothing new in Jharkhand-based Naxals operating in West Bengal, they said in earlier incidents, Maoists after carrying out a major attack in Jharkhand used to cross over to West Bengal, which they considered as "safe heaven".