DOHA: Peace talks between the Taliban and the Afghan government opened in Qatar on Saturday, marking what US Secretary of State Mike Pompeo heralded as a "truly momentous" breakthrough in nearly two decades of relentless conflict.

Negotiations will be arduous and messy, delegates acknowledged at an opening ceremony in Doha, and are starting even as deadly violence continues to grip Afghanistan.

"We will undoubtedly encounter many challenges in the talks over the coming days, weeks and months," Pompeo said as he called for the warring sides to "seize this opportunity" to secure peace.

"Remember you are acting not only for this generation of Afghans but for future generations as well, your children and your grandchildren."

Nineteen years since the US-led invasion that toppled the Taliban, Afghanistan's war still kills dozens of people daily and the country's economy has been devastated, pushing millions into poverty. Abdullah Abdullah, who was previously Afghanistan's chief executive and is heading the peace process for Kabul, said 12,000 civilians have been killed and another 15,000 wounded just since the US signed a withdrawal agreement with the Taliban on February 29. Abdullah called for an immediate, humanitarian ceasefire -- but his plea went unanswered by Taliban co-founder Mullah Abdul Ghani Baradar, who made no mention of a truce in his opening remarks. The Taliban have long worried that reducing violence could lessen their leverage.

Instead, Baradar repeated the insurgents' message that Afghanistan should be run according to Islamic law, highlighting what likely will be the main sticking point in negotiations.

A comprehensive peace deal could take years, and will depend on the willingness of both sides to tailor their competing visions for Afghanistan and the extent to which they can agree to share power.

The Taliban want to reshape Afghanistan as an Islamic "emirate", while the adminstration of President Ashraf Ghani wants to maintain the Western-backed status quo of a constitutional republic that has enshrined many rights, including greater freedoms for women.

Norwegian Foreign Minister Ine Eriksen Soreide urged all sides to include "women, victims and minorities and other stakeholders" in the process, saying such inclusivity is the key to an enduring accord.

Four of the 21 people on the Kabul negotiating team are women. Not surprisingly, the Taliban, who stripped women of all basic freedoms while in power from 1996-2001, had no females on their team.

In a statement, Ghani called for "a lasting and dignified peace" that preserved "the achievements of the past 19 years".

Kabul negotiator Habiba Sarabi told AFP the start of talks had been "very positive".

"Everybody including Secretary Pompeo shared their solidarity, from the Taliban side also. ... We're on the way to building the trust," she said.

Zalmay Khalilzad, the US envoy who led talks with the Taliban, said the timetable for foreign troops to quit Afghanistan by May remained on track, and that he wanted a comprehensive ceasefire before then.

"The hope is ... there will be a reduction of violence immediately," leading eventually to a permanent ceasefire, Khalilzad said.

He cautioned that Washington would not underwrite a future Afghan state that was not in line with "universal values" -- including women's rights.

"There is no blank cheque," Khalilzad said.

The US-backed negotiations come six months later than planned owing to disagreements over a controversial prisoner swap agreed in February.

They are being held in a luxury hotel in Doha, where chairs were dotted at socially distanced intervals facing a banner emblazoned with the words "Afghan Peace Negotiations" in four languages.

Doha also hosted the signing of the US-Taliban deal in February that paved the way for peace talks.

The Taliban claimed "victory" after that deal, and see their bargaining position as stronger now than at any time in the last two decades.

A who's who of international stakeholders in the Afghanistan conflict spoke at the opening ceremony, including UN Secretary-General Antonio Guterres and NATO chief Jens Stoltenberg.

Qatar has quietly guided the process, which has been complicated by violence in Afghanistan and the coronavirus crisis. Doha's chief mediator Mutlaq al-Qahtani stressed "the power of diplomacy".

Doha invited the Taliban to open a political office in 2013 and helped broker February's US-Taliban deal.

Since that agreement, the insurgents have continued to launch daily attacks and targeted assassinations. The Afghan defence ministry told AFP clashes had been reported in more than 20 provinces in the past 24 hours. Nonetheless, the Taliban on Saturday said they had released 22 Afghan troop prisoners as a "goodwill gesture" to mark the start of talks.