The Special Task Force of Kolkata police is yet to pinpoint the location of the SIM cards used to call up the three businessmen, which include two shoe barons and a hotelier.

Senior IM commanders reportedly called the three a number of times last week, demanding Rs 35 crore from each of them as protection money. The caller also demanded the release of Aftab Ansari, the mastermind of American Center attack and the abduction of another city industrialist Partho Roy Burman. The caller allegedly said the money would be used to help Ansari out and threatened to kill the industrialists if they refused to pay up.

“We have given them tips regarding their protection. They have security and we will increase vigil,” Chief Secretary Asok Mohan Chakraborti said today. According to sources, representatives of the three businessmen met top police and administrative officers at the Writers’ Buildings yesterday.

“The industrialists have their private bodyguards, but we are also providing plainclothes policemen round-the-clock for each of them. Additional security cover has also been provided to their kin who may also be targetted,” said a senior police officer.

The advisory issued to the industrialists include restrictions in movement to unprotected public places for them and their kin. Sources said they have been advised not to make unplanned journeys within the country or abroad. Their movement plans for the day will have to be submitted to Kolkata police.

The dos and don’ts also include avoiding to venture out of their homes at night or to visit crowded places. “They have been told to avoid public functions, including marriage ceremonies, unless very necessary and they should ensure the venue is a secured place. We are keeping an eye on their phone calls,” a senior police officer said.

Police sources said similar ransom calls were made earlier to businessmen in Kolkata and Howrah and some had paid up.