Khulna University Vice-Chancellor Prof Dr Mahbubur Rahman, professors Ashit Baran Ghose, Sajib Ghose, and Shushato Biswas and journalist Gouranga Nandy of Dainik Janakantho are among those who received the threats in last one week.

Meanwhile, Abir Hasan, who identified himself as an operation commander of Janajuddho, faxed to three local newspaper offices on Thursday night denying his party's involvement in such acts during the last one month.

A group of drug addicts are involved in the crime, Khulna Metropolitan Police (KMP) commissioner said, adding, "We are trying hard to track down the criminals."

While demanding tolls, most of the callers are using the name of Janajuddho founder Dada Tapan who is reportedly away from such activities now, a senior officer of Detective Branch of KMP said, adding that they have identified 35 cell phone numbers for investigation.

Expressing grave concern at the rise of extortion in the city, Khulna Chamber of Commerce and Industry President Shaharuzzaman Martuza said it has seriously affected trade activities.