The so-called Doha agreement was signed in February 2020 and set a date for the US to withdraw its troops.
Gen Frank McKenzie said the deal had a "really pernicious effect" on the Afghan government and military.
Defence Secretary Lloyd Austin agreed, saying the agreement had helped the Taliban get "stronger".
In addition to setting a withdrawal date, the Doha agreement included broad obligations on the Taliban to take steps to prevent groups such as al-Qaeda from threatening the security of the US and its allies.
