Taliban: We killed 4 U.S. troops at Afghan air base Updated 3:05 a.m. KABUL, Afghanistan The Taliban claimed responsibility Wednesday for an attack in Afghanistan that killed four American troops just hours after the insurgent group announced it would hold talks with the U.S. on finding a political solution to ending the nearly 12-year war in the country. The deadly attack underscores the challenges ahead in trying to end the violence roiling Afghanistan via peace negotiations in Qatar with militants still fighting on the ground. Afghan military officially takes control of country's security Taliban spokesman Zabiullah Mujahid said the insurgents fired two rockets into the Bagram Air Base outside the Afghan capital, Kabul, late on Tuesday. American officials confirmed the base had come under attack by indirect fire -- likely a mortar or rocket -- and that four U.S. troops were killed. The attack came as the Taliban opened a political office in the Qatari capital of Doha, and announced they were ready for peace talks. The decision was a reversal of months of failed efforts to start negotiations while Taliban militants intensified a campaign targeting urban centers and government installations across Afghanistan. The Taliban announcement followed a milestone handover in Afghanistan earlier Tuesday, as Afghan forces formally took the lead from the U.S.-led NATO coalition for security nationwide. It marked a turning point for American and NATO military forces, which will now move entirely into a supporting role. It also opened the way for the withdrawal of most foreign troops in 18 months. President Obama cautioned that the peace talks with the Taliban would be neither quick nor easy, but called their opening a political office in Doha was an "important first step toward reconciliation" between the Islamic militants and the government of Afghanistan. In setting up the office, the Taliban said they were willing to use all legal means to end what they called the occupation of Afghanistan -- but did not say they would immediately stop fighting. American officials said the U.S. and Taliban representatives will hold bilateral meetings in coming days. Afghan President Hamid Karzai's High Peace Council is expected to follow up with its own talks with the Taliban a few days later.