The assailants fired upon Javeed Ahmad Dar near his residence at Brazloo Jageer area of the south Kashmir district at around 4.30 pm, officials said.
Forest Minister Chaudhary Lal Singh and Industries Minister Chander Prakash had attended the rally.
An altercation broke out between worshippers, who were coming out of a mosque in Handwara town of Kupwara district, and Army personnel, who were recording videos.
Arrangements are being made at Bejibehara, the leader's hometown, for his last rites.
Ill-health forced Bihar Chief Minister Nitish Kumar to cancel his scheduled visit to Chennai on Tuesday, where he was invited by his Tamil Nadu counterpart MK Stalin, a key aide of the Janata Dal-United leader said.
A basic outline and roadmap for Opposition unity are likely to be deliberated upon with the contentious issue of seat sharing and leadership questions to be avoided for now.
Intense clashes had rocked Kashmir Valley in 2016 following the death of Hizbul Mujahideen commander Burhan Wani in July that year, resulting in the death of over 85 people.
"When the people of BJP (Bharatiya Janata Party) talk of Article 370, they talk of technical integration. We have to make them understand that we also want that Jammu and Kashmir should fully integrate with India emotionally," she said.
Calling the FIR against the army as 'unfortunate', Lt Gen Anbu said that there should have been generic FIR in the matter.
'The government can do many things to improve the situation in Kashmir.'
The Bharatiya Janata Party, a coalition partner in Mufti Mohammad Sayeed-led government in Jammu and Kashmir, on Sunday criticised the controversial decision to release hardline separatist leader Masarat Alam and said its ministers and legislators will meet to discuss the party stand over the "unilateral" step.