Mullah Abdul Ghani Baradar, a co-founder of the movement, was released last year from a Pakistani jail where he had been held since his arrest in a joint Pakistani-CIA operation in 2010. His release was seen as a first concession to the Taliban after Khalilzad's appointment in September and the start of his talks with the insurgents.
Baradar arrived on Sunday in Doha, the capital of Qatar, from Pakistan. His presence in Doha, where the Taliban maintain a political office, and his lead role in the talks with Khalilzad is considered significant because of his stature within the Taliban, who control or hold sway over nearly half of Afghanistan.
Taliban spokesman Zabihullah Mujahid raised expectations ahead of talks with Khalilzad, telling The Associated Press "there is a possibility we will reach some results."
Following his release, Baradar had circulated an audio tape promising Taliban fighters he would have a greater presence within the movement.
Khalilzad described the Taliban interlocutors in this round of talks as "more authoritative" — an apparent reference to Baradar — and tweeted that this could be "a significant moment" in the talks. He also gave a shoutout to Qatar for hosting the talks and to Pakistan for facilitating some of the Taliban delegation's travel.
Khalilzad also tweeted about his luncheon meeting with Baradar, saying it was his first meeting with the Taliban co-founder.
The Afghanistan Analysts Network, an independent Kabul-based research organization, describes Baradar as "one of the most experienced Taliban commanders" who had been with the group since its earliest days.
"Baradar is a highly experienced military commander and keen political strategist and played a major role in organizing the insurgency in its formative years," the research group said in a report following Baradar's release in October.
Past rounds of talks between Khalilzad and the Taliban have focused on the withdrawal of American troops in exchange for guarantees that Afghanistan will not be used again as a staging area for attacks on the United States. The U.S. envoy is also expected to pressure the Taliban to hold direct talks with the Kabul government.
The Taliban, who had harbored al-Qaida and its leader Osama bin Laden, ruled Afghanistan before U.S. forces invaded in October 2001 following the 9/11 attacks. The Taliban have made a major comeback in recent years, and today carry out near-daily attacks on Afghan security forces. They view the U.S.-backed government in Kabul as a dysfunctional Western puppet and have refused repeated offers to negotiate with it.
However, former Afghan President Hamid Karzai recently told the AP that the Taliban would talk with Afghan government officials on condition they are part of a larger group of prominent Afghan figures — similar to a gathering held earlier this month in Moscow.
Karzai attended the meeting in Russia, as did Afghan opposition figures, but no one from the Kabul government was there.
Since his appointment as Washington's peace envoy, Khalilzad has crisscrossed the region, meeting the Taliban on several occasions, as well as powerbrokers in Kabul, including Afghan President Ashraf Ghani.
He has also been to Pakistan, India, Russia and China and held meetings with NATO and EU officials. Last week, he was in Turkey for talks with government officials as well as Zamir Kabulov, Russia's envoy to Afghanistan.
Ghani has called a Loya Jirga, a traditional gathering of political and tribal leaders, for next month to draw up the government's negotiating position for talks with the Taliban, though he has yet to put together a negotiating team that would have wide support.
Khalilzad has said he hopes to broker a "roadmap" for Afghanistan, but the current talks are focused on safeguarding America's national interests and security. The U.S. envoy has said it is up to the Afghans to determine their country's future.
Gannon reported from Islamabad. Associated Press writer Matthew Lee in Washington contributed to this report.