Extortion calls tagged with abduction threats have sent a shiver up the spine of the city’s business circles and caught police on the hop.

Amid the deepening mystery surrounding the abduction and release of IT professional Sandipan Das came the news that two prominent business houses have lodged police complaints stating that they had been receiving extortion calls for over a week.

The callers have allegedly threatened that if the extortion amount — ranging from Rs 20 crore to Rs 40 crore — is not paid, the owners would be abducted.

“We have received two complaints and started cases. We are examining the numbers from where the calls came,” said Damayanti Sen, the deputy commissioner of police, detective department.

According to detective department sources, the owners of two other business houses have received such calls but haven’t yet lodged any complaint.

“The complaints were lodged on Friday. The owners of the business houses have told us that they have been receiving the calls for over a week,” said an official.

“The callers, however, haven’t specified how the money has to be paid. They told the owners to keep the amount ready and wait for further orders,” the officer added.

Home secretary Ardhendu Sen said at the Writers’ Buildings that “necessary security cover” had been provided to the complainants. “They also have their own security guards,” added Sen.

Following the twin complaints, police commissioner Gautam Mohan Chakrabarti has instructed the Special Task Force (STF) — formed to deal with high-profile abductions and terrorist activities — to take up the cases.

“The threat calls came both to the offices and houses of the businessmen. Our initial probe suggests the calls were from Karachi,” said an STF official. “Voice recorders have been installed in the offices and houses of the complainants. We have recorded the voice of the caller.”

The sleuths suspect the calls came from Aamir Reza Khan, a Lashkar-e-Toiba operative and an Aftab Ansari aide. Aamir, a Calcutta boy, was also a key accused in the American Center attack.

“The caller identified himself as Aamir and we have reasons to believe that he was Aamir Reza Khan,” said an officer.

Indian security agencies believe Aamir was one of the founder members of the Indian Mujahideen, a Lashkar-backed module that has carried out a series of blasts in Jaipur, Bangalore and Hyderabad.

Home secretary Sen did not comment on the nature of the calls and the findings of the preliminary inquiry.

“There are reports that the calls came from Karachi but it’s not clear till now. We also cannot say anything on whether those were international or local calls… Investigations are being conducted,” said Sen.