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 decade-long Afghan war. The chance to start a dialog came as the Islamist insurgent group 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. But the dramatic announcements were marred hours later by yet more violence, with four Americans killed by insurgent fire at the sprawling Bagram air base, north of Kabul, military officers said. The Taliban had broken off contact with the Americans last year and had refused to negotiate with the government in Kabul. But spokesman Zabiullah Mujahid told AFP the office was intended \"to open dialog between the Taliban and the world\". With US officials telling reporters that discussions would begin in coming days, President Barack Obama called the talks an \"important first step\" but warned of a long and bumpy road ahead. \"An Afghan-led and Afghan-owned peace process is the best way to end the violence and to ensure lasting stability in Afghanistan and the region,\" Obama said on the sidelines of the Group of Eight summit in Northern Ireland. Obama insisted the Taliban would have to renounce ties to Al-Qaeda, halt violence and commit to the protection of women and minorities, and warned that US-led NATO forces remain \"fully committed\" to battling Al-Qaeda. The Taliban, who were driven from power in the wake of the September 11, 2001 attacks by US-backed rebels, have since mounted a guerrilla war against the Afghan government and maintain rear bases in Pakistan. Pakistan, which has battled its own Islamist insurgency but is widely seen as quietly backing the Afghan Taliban, said it welcomed the peace talks. UN Secretary General Ban Ki-moon also welcomed the talks, with a spokesman saying dialog is \"the only way to end the violence.\" With the war at a stalemate, 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 most international forces leave in the course of next year. In parallel, US envoys are attempting to open a dialog 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. A US official said American and Taliban envoys would meet in Doha \"in a couple of days,\" after which the Taliban would meet with a \"High Peace Council\" set up by Karzai to conduct the negotiations. 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 they 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 the Taliban envoys in Doha had been authorized to talk by Mullah Omar, the main Taliban figurehead, and that Haqqani\'s group was \"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. Officials said this week\'s ground-breaking meeting would amount to \"an exchange of agendas,\" followed by another within about two weeks. The Taliban said they 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, 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 security handover ceremony Karzai attended. 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 to maintain security, and the 98,000 foreign troops still in Afghanistan will retain an important function in training, logistics, air support and in combat emergencies.