Burhanuddin Rabbani, the head of Afghanistan's High Peace Council, was killed by an unidentified attacker at his home in Kabul on Tuesday.
Rabbani was the President of Afghanistan twice, serving between 1992 and 1996, and then again after the fall of the Taliban government in 2001. He was appointed to head the Peace Council by current president Hamid Karzai last year.
Initial reports suggest that Rabbani was killed by a suicide bomber, who attacked the leader's heavily fortified home near the U.S. embassy in the capital.
Rabbani has been martyred, Mohammed Zahir, head of the Criminal Investigation Department of the Kabul Police, told Reuters.
As head of the High Peace Council, Rabbani had been charged with ending the near-constant violence and sectarian fighting in Afghanistan. He was to broker peace talks between Karzai's government and the Taliban, although stubbornness on the both sides had proved the task to be futile.
The former-president's death is the latest blow to stability and security of Afghanistan, which is preparing for a full withdrawal of U.S. troops by 2014.
Last week, Taliban and Haqqani network insurgents staged a massive attack on Kabul, which lasted 20 hours and resulted in the deaths of more than a dozen people.
During the attack, five armed militants planted high up on a building next to the U.S. embassy fired down upon the embassy with rockets and machine guns. Local police and Black Hawk helicopters fired at the gunmen by the embassy, killing two. The other three insurgents hunkered down in the building, using hand grenades to keep local and NATO troops from getting too close.
Contemporaneously, there were attacks on NATO headquarters, a police station and an intelligence office in Kabul, which were followed by at least three attempted suicide bombings near the airport.