Sayyaf claimed and claims he is a vituperative opponent of the Taliban movement, which is the reason he officially joined the Northern Alliance, despite his religious and ideological affinities with the Taliban and Al-Qaeda. Sayyaf was initially the only Pashtun leader in the Northern Alliance fighting against the Taliban. Sayyaf is rumored to have helped Arab suicide assassins to kill the Northern Alliance leader, Ahmad Shah Massoud. He is also rumored to have helped during their preparations, raising suspicion he was involved in killing Massoud. Sayyaf's forces participated in the Northern Alliance's capture of Kabul during the 2001 U.S. invasion of Afghanistan.