Raman Bhalla said he approached police soon after he received the letter.
Police have registered a First Information Report (FIR) after a senior Congress leader received a letter from Hizbul Mujahideen threatening to target mainstream politicians of the Jammu region, including Union minister Jitendra Singh, if they did not quit politics, officials said on Sunday.
The two-page letter, written in Urdu on the terror group's letter pad, was delivered by post to senior vice president of Jammu and Kashmir Congress and former minister Raman Bhalla at his headquarters on Friday, the officials said.
"We have registered a case under relevant sections of the law and further investigation is on," Senior Superintendent of Police, Jammu, Shridhar Patil told PTI.
Mr Bhalla said he approached police soon after he received the letter as a thorough investigation is required into the incident.
"We will not be cowed down by such threats from anti-national elements. We have stood against the terror unleashed at the behest of Pakistan in Jammu and Kashmir over the past three decades and will continue to perform our duties to make J-K free of terrorism, peaceful and prosperous," he said.
He said the Congress history is replete with the "blood of martyrs" and "I would be happy to follow the footsteps of our great leaders and sacrifice my life for the nation".
The letter, signed by Hizbul Mujahideen terrorist commander, named 17 senior politicians of various national and regional parties including Union minister Singh, Bhalla, J-K BJP president Ravinder Raina, former deputy chief minister Nirmal Singh, National Conference provincial president Devender Singh Rana, Dogra Swabhiman Sangathan leader Choudhary Lal Singh and National Panthers Party chairman Harsh Dev Singh besides several other former ministers, legislators and RSS functionaries.
"We warn you to renounce politics and support our cause for freedom otherwise death warrants have been issued against you. No security cover will safeguard you from us," the letter read, adding "the work has already started and those who can attack Parliament or Red Fort can kill you as well".
"In coming days, no Indian or politician supporting India will be left alive in Kashmir. Half of Jammu is already with us but there are some politicians who are an obstacle to our cause for freedom," the letter said.
Reacting to the threat, JKNPP chairman Harsh Dev Singh demanded a high-level probe and said it seems to be part of a conspiracy to browbeat the opposition.
"I have raised security concerns many times after receiving threats from BJP leaders in the past but instead of taking action on my complaint, I was deprived of security cover by the administration," he said, adding he is only having one personal security officer despite being an MLA for three successive terms and a former minister while as an ordinary BJP worker is given 10 security guards with accommodation and vehicle for movement.
"The probe is necessary to unravel the truth behind the threat," he said.