In this file photo taken on June 25, 2021 President of Afghanistan Ashraf Ghani meets with US President Joe Biden in Washington, DC, on June 25, 2021.
The Afghan-born Khalilzad, speaking for the first time since his resignation was announced on October 18, also expressed reservations about the decision by the Biden administration to lift conditions on the withdrawal deal he had negotiated with the Islamist insurgents during the administration of President Donald Trump.
The agreement signed on February 29, 2020 between Washington and the Taliban -- which excluded Ghani's government in Kabul -- paved the way for the US to end its longest war.
But it was "a conditions-based package" that included negotiations between the insurgents and Kabul, as well as a permanent, comprehensive cease-fire, Khalilzad said.
Once in the White House, however, President Joe Biden decided "to do a calendar-based withdrawal," without regard to those conditions, he said.
"That was a decision made way above my pay grade," he added.
Talks between the insurgents and Kabul had begun but were dragging, and Washington feared the Taliban would resume attacks on US forces if they stayed in the country much longer -- a situation Khalilzad acknowledged as he admitted things did not work out the way he had wanted.
He placed most of the blame on Ghani, who Khalilzad said never agreed to share power with the Taliban.
"They preferred the status quo to a political settlement," he said of the Kabul government.
"And then when it became clear that the US was leaving, then they -- they miscalculated the effects of the continuing war. They were not serious about the political settlement.
"It's my judgment that we didn't press him hard enough. We were gentle with President Ghani. We used diplomacy. We encouraged him."
He said that under the original conditional withdrawal agreement, the Taliban would have eventually agreed to power-sharing, though his evidence for that was unclear.
Biden had set a departure date of August 31 for the final withdrawal.
But in the months and weeks leading up to that date the Taliban offensive surged. On August 15 Ghani fled Kabul as government authority crumbled and the Taliban marched into the capital city.
Khalilzad -- derided in Afghanistan for, among other things, cutting Kabul out of the US-Taliban deal, and who has also been much criticized in Washington since the takeover -- has blamed Ghani before.
He told the Financial Times in September that Ghani's abrupt exit scuttled a deal in which the Taliban would hold off entering Kabul and negotiate a political transition.
Ghani, who sought safety in the United Arab Emirates, has apologized for how his government ended but said he left on the advice of palace security to avoid bloody street fighting.
The Taliban had been demanding the resignation of Ghani as part of any transitional government.
Ultimately, the Islamists named a caretaker government that has no non-Taliban nor women and that includes US-designated terrorists.