The U.S. special envoy Zalmay Khalilzad and Taliban officials reported "significant progress" in talks in Qatar aimed at resolution to the 17-year conflict in Afghanistan, but no agreement has been announced. In a series of tweets, U.S. Special Representative Zalmay Khalilzad wrote "meetings have been more productive than they have been in the past" but did not offer any details.

Secretary of State Mike Pompeo tweeted Khalilzad's report of "significant progress" is "encouraging news."

Taliban spokesman Zabihullah Mujahid in a statement Saturday said the Taliban are steadfast in their demand that no substantive progress is possible without a troop withdrawal. But he did acknowledge progress.

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"This round of negotiations revolving around the withdrawal of foreign troops from Afghanistan and other vital issues saw progress; but since issues are of critical nature and need comprehensive discussions therefore it was decided that talks about unsolved matters will resume in similar future meetings," Mujahid said.

President Trump ordered the Pentagon in December to begin planning a major drawdown of the nearly 7,000 U.S. troops in Afghanistan. There was no mention Saturday of a possible timeline for withdrawing U.S. troops.

These talks are between U.S. representatives, not the Afghan government, and the Taliban.

It wasn't clear whether Khalilzad is seeking written guarantees from the Taliban that they will distance themselves from al Qaeda operatives, including Ayman al Zawahiri, who live among them or at the very least have safe passage and havens within territory they control.

Zawahiri, an Egyptian, took over the leadership of al Qaeda following the 2011 killing of Osama bin Laden in Abbottabad, Pakistan by U.S. Navy SEALS.

There are also believed to be a number of Arabic-speaking jihadis associated with the Haqqani network, considered the most lethal of the Taliban fighters in Afghanistan.

It wasn't clear how the U.S. could verify Taliban promises to ensure Afghan territory is not again a staging arena for attacks outside its borders.

There was also no indication that the Taliban would agree to a cease-fire, which Khalilzad has been seeking, or when the Taliban would hold direct talks with the Afghan government, something they have continued to reject.

The Haqqanis did send three representatives to a meeting with Khalilzad in the United Arab Emirates last month, an indication that they are in sync with the Taliban leadership conducting the negotiations.

It wasn't immediately clear if any were in attendance this past week in Qatar.

The Taliban negotiating team that met this week in Qatar with Khalilzad were all senior members of the movement. They included Salam Hanafi, Muhammad Hanif and Mohammad Zahid Ahmadzai __ all members of the Taliban leadership council __ Suhail Shaheen, spokesman for the Taliban's Qatar office, Shahabuddin Dilawar, Muhammad Fazl and Khairullah Khairkhwah.

Both Fazl and Khairkhwah were among five Taliban freed from the U.S. prison at Gunatanamo Bay in 2014 in exchange for U.S. Sgt. Bowe Bergdahl who had been captured by the Taliban in 2009 after he wandered off his base.

These negotiations are the most significant held to date.

Last week, the Taliban threatened to walk away from talks, accusing Washington of seeking to "expand the agenda" - presumably a reference to U.S. demands that the insurgents hold direct talks with Kabul.

Khalilzad has said that any peace talks must include the Afghan government and a comprehensive cease-fire.

Khalilzad has met with the Taliban on a number of occasions in recent months in the latest bid to end America's longest war. The U.S. invaded Afghanistan after the Sept. 11, 2001 attacks to topple the Taliban, who were harboring Osama bin Laden and al Qaeda. The Taliban have staged a comeback in recent years and today hold sway over nearly half the country.