The Taliban have steadfastly refused to negotiate with the Afghan government, whom they dismiss as 'puppets'
The US and the Taliban have drafted the framework of a deal which could pave the way for peace talks with Kabul, Washington's main negotiator was quoted as saying Monday, but major hurdles including a ceasefire and a withdrawal of foreign forces remain.
The comments by special envoy Zalmay Khalilzad to the New York Times are the clearest signal yet from a US official that talks between Washington and the militants are progressing, igniting hopes of a breakthrough in the grinding 17-year conflict.
Khalilzad has been leading a months-long diplomatic push to convince the Taliban to negotiate with the Afghan government, but the militants have steadfastly refused, dismissing authorities in Kabul as "puppets".
The flurry of activity culminated in an unprecedented six straight days of talks in Qatar last week, with both the US and the Taliban citing progress over the weekend.
"We have a draft of the framework that has to be fleshed out before it becomes an agreement," Khalilzad, who arrived in Kabul Sunday to update Afghan authorities on the talks, was quoted as saying by the Times.
He told Afghan media that Washington and the insurgents had "agreed to agreements in principle on a couple of very important issues", and said Afghans must "seize the opportunity", according to comments released by the US embassy in Kabul.
Experts quickly hailed the development as a milestone, noting it indicated willingness on both sides to find a way out of the conflict.
Acting US Defence Secretary Patrick Shanahan described the talks as "encouraging".
However there is still no accord on a timetable for a US withdrawal or a ceasefire -- major issues on which previous attempts at negotiations have foundered.
On Saturday Taliban spokesman Zabihullah Mujahid said that without a withdrawal timetable, progress on other issues is "impossible".
- 'Good faith' -
Khalilzad confirmed the Taliban had acceded on one major issue for the US: safe havens.
"The Taliban have committed, to our satisfaction, to do what is necessary that would prevent Afghanistan from ever becoming a platform for international terrorist groups or individuals," he told the Times.
He gave no further details, but the statement gave weight to reports last week that the Taliban had agreed to oppose Al Qaeda and the Islamic State group in Afghanistan.
The US invasion of 2001 was driven by the Taliban's harbouring of Al Qaeda, but more than 17 years later the jihadist group appears diminished in the region.
Islamic State, however, is a growing and potent presence in Afghanistan, where it is fighting a fierce turf war with the Taliban in some areas.
Analyst Michael Kugelman of the Wilson Center in Washington, DC said such a move had long been a major ask of the US -- but noted it was more of a "conciliatory gesture" than a concession.
"The Taliban has never been a friend of ISIS, and Al-Qaeda has become a shadow of its former self," he told AFP.
Even so "it signals, at least at this point, that the insurgents are willing to negotiate in good faith and agree to a key US demand".
- 'Clear, hard assurances' -
Afghan authorities have warned that any deal between the US and the Taliban would require Kabul's endorsement.
"I call on the Taliban to... show their Afghan will, and accept Afghans' demand for peace, and enter serious talks with the Afghan government," President Ashraf Ghani said in a televised address Monday.
US President Donald Trump's clear eagerness to end America's longest war has also weighed heavy on the discussions, and Ghani warned against rushing into a deal, citing violence following the Soviet withdrawal in 1989.
"We want peace, we want it fast but we want it with a plan," he said.
"No Afghan wants foreign troops to remain in their country indefinitely. No Afghan wants to face suicide attacks in hospitals, schools, the mosques, and parks."
Civilians continue to pay a terrible price for the Taliban insurgency, with some estimates showing the Afghan conflict overtook Syria to become the world's deadliest last year.
Ghani's office said Khalilzad had reassured the government that the negotiations in Qatar remain focused on bringing the insurgents to the table for talks with Kabul.
The palace said Khalilzad confirmed no agreement had been made on a withdrawal or a ceasefire.
NATO combat troops left Afghanistan in 2014, but thousands remain in training, support and counter-terrorism roles. Trump has said he wants to pull out half the remaining 14,000 American troops, according to US officials.
Kugelman said the process could yet collapse over a withdrawal.
"Who's to say the Taliban won't decide to seize on the resulting battlefield advantage and take up the fight anew?" he said.
Afghan security forces are already taking staggering losses, with 45,000 killed since late 2014, and morale is low.
"There will need to be clear, hard assurances that any troop withdrawals take place only after the Taliban has begun talks with the Afghan government," Kugelman continued.
Underlining the parlous backdrop to the talks, the Taliban Monday claimed to have killed or wounded 33 US and Afghan forces in two recent incidents, according to the SITE monitoring group. The Taliban routinely exaggerates its attacks, and NATO denied the claims.
The Taliban and US officials have agreed to continue negotiations, though no date has been publicly announced.