In the past two weeks, three influential Pakistani militants based in Afghanistan have been assassinated, whilst another Pakistani militant group has been targeted in a deadly raid by Afghan special forces. The apparent crackdown comes as negotiations between US and Afghan Taliban officials, aimed at bringing an end to the 18-year-long conflict, appear to be leading towards an agreement. One militant source told the BBC he believed the deaths were the result of a secret pact between American and Pakistani forces. Pakistan is believed to have played an important role in facilitating the discussions. In the latest incident, Shehryar Mehsud, leader of a breakaway faction of the Pakistani Taliban, was killed in the eastern province of Kunar when a remote control bomb exploded close to his home. He had numerous rivals within militant circles, but they have denied involvement in his death, whilst members of his group told the AFP they believed Pakistani intelligence services were responsible. The Pakistani Taliban and Afghan Taliban are separate organisations - focussed on carrying out attacks only within their own countries. Various factions of the Pakistani Taliban established bases in eastern Afghanistan, following military operations against them in Pakistan. It is alleged that the Afghan security services developed links to some of the groups - to counteract Pakistani support for the Afghan Taliban, which has been waging a long-running insurgency aimed at forcing out the Afghan government, backed by US-led forces. Both countries officially deny supporting militant groups. Earlier this month, two senior Pakistani Taliban commanders were killed in mysterious circumstances in the Afghan capital Kabul. Meanwhile, on Monday reports emerged of a raid on the Hizbul Ahrar Pakistani militant group by Afghan forces in the eastern province of Nangarhar. Members of Hizbul Ahrar were shocked at the raid, saying they previously believed they would not be targeted by Afghan security forces, as they have not carried out attacks within Afghanistan.