"It is time for Holly [the ambassador's wife] and I to leave #Afghanistan," Bass wrote on Twitter.
The outgoing ambassador expressed hope that Afghanistan's citizens and leaders would "find strength in unity, put aside their differences, and work together to negotiate a political settlement with the Taliban."
A US State Department official told The New York Times on conditions of anonymity that it was typical for US ambassadors to spend two years only in Kabul, given the "high-stress nature of the job." The official added that Bass' departure had been long-planned and was not a result of any conflict.
His departure comes amid Washington's attempts to agree on a peace deal with the Taliban movement since US Special Representative for Afghanistan Zalmay Khalilzad has recently arrived in Qatar for a new round of bilateral talks.
The United States wants the Taliban to cut ties with terrorists and engage in closer cooperation with the Afghan government, thus enabling US troops withdrawal. Many rounds of peace talks have been held, bringing no significant result.