Four US troops killed in Afghanistan

The attack also occurred as the Taliban agreed to hold direct peace talks with the United States and government of Afghanistan and set up a new political office in Doha, Qatar.

As part of the agreement to start the talks, the Taliban said it was committed to the peace process and would not allow Afghan soil to be used to threaten other nations.

The two steps are an important part of the U.S. and NATO plan to wind down the war in Afghanistan by the end of 2014, when the Afghans are set to be fully in charge of security.