US envoys will launch talks this week with the Taliban, officials announced Tuesday, in a tentative first step towards finding a negotiated escape from the 12-year-old Afghan war.

The opportunity to open a dialogue came as the Islamist militia opened a political office in the Qatari capital Doha to act as an embassy to its foes in Washington and President Hamid Karzai's Afghan administration.

It also coincided with NATO's formal transfer of responsibility for Afghan security to Karzai's forces. The US-led international combat mission is due to wind down next year, with Afghanistan still in the grip of fighting.

The Taliban had broken off contact with the Americans last year and has refused to negotiate with Kabul, but spokesman Zabiullah Mujahid told AFP the office was intended "to open dialogue between the Taliban and the world".

With US officials telling reporters that contact would be established in "a couple of days," Secretary of State John Kerry said of the office opening: "It's good news. We are very pleased with what is taking place."

The Taliban, which was driven from power in Kabul in the wake of the 9/11 attacks in 2001 by US-backed rebels, has since mounted a guerrilla war against the new government and maintains rear bases in Pakistan.

A huge US-led NATO army has proved incapable of defeating the insurgency and is concentrating on training Afghan government troops to take charge when international forces end combat operations in the course of next year.

In parallel, US envoys are attempting to establish a dialogue with the main Taliban faction, in the hope of convincing it to repudiate ties to the Al-Qaeda extremist network and to reach a political deal with Karzai.

"I think the US will have its first formal meeting with the Taliban, and the first meeting with the Taliban for several years, in a couple of days in Doha," a US official told reporters, speaking on condition of anonymity.

"I would expect that to be followed up within days by a meeting between the Taliban and the High Peace Council, which is the structure that President Karzai has set up for talks of this nature," the senior source said.

In opening its mission, the Taliban did not explicitly renounce Al-Qaeda, which prior to 9/11 and the US intervention had bases in Afghanistan, but it did vow not to allow attacks to be launched from Afghan soil.

This proved a sufficient first step for US officials, and State Department spokeswoman Jen Psaki said that an eventual disavowal of Al-Qaeda ties by the Taliban was only an "end goal of the process."

Psaki could not say when the meeting would take place, but said Ambassador James Dobbins, US special representative for Afghanistan and Pakistan, would leave Washington later Tuesday bound for Doha via Ankara.

The divided Afghan insurgency could complicate talks, amid US doubts as to whether the powerful "Haqqani network" of warlord Jalaluddin Haqqani, a former CIA asset turned Al-Qaeda ally, was ready to embrace negotiation.

US officials said that the Taliban envoys in Doha had been authorized to talk by Mullah Omar, the main Taliban figurehead, and that Haqqani's group is "a fully subordinate part of the overall insurgency."

But General Joseph Dunford, the US commander in Afghanistan, said he was skeptical the Haqqanis would back a peace deal.

"I would just tell you that all I've seen of the Haqqanis would make it hard for me to believe they were reconcilable," he told reporters by video link from Kabul.

Officials said this week's ground-breaking meeting would amount to "an exchange of agendas," followed by another within about two weeks.

"We'll tell them what we want to talk about and they'll tell us what they want to talk about and we'll both adjourn and consult on next steps, and then have another meeting in a week or two later," a US official said.

For their part, the Taliban said: "We support a political and peaceful solution that ends Afghanistan's occupation, and guarantees the Islamic system and nationwide security."

Karzai, who has long called for peace talks, attended the security handover ceremony and said he had ordered government envoys to travel to Qatar to try to open negotiations.

He pledged that Afghan forces were ready to take on the insurgents, but the enduring threat was underlined when a bomb targeting a lawmaker killed three people just before the ceremony.

The turnover of the last districts from NATO to Afghan control included areas in the south and east where the Taliban are at their strongest.

Doubts remain over the ability of Afghan forces, and the 98,000 foreign troops still in Afghanistan will retain an important function in training, logistics, air support and in combat emergencies.

Concern over capacity has been fueled by high rates of desertion and fears for the future of foreign aid post-2014.

"The reality is Afghan forces are not dreadful, but they're probably not sufficiently capable to drive the war to a conclusion," Stephen Biddle, professor of international affairs at George Washington University, told AFP.

"My guess is they will be able to maintain the stalemate, provided the US pays their bills."

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