Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. US Defense Secretary Arrives in Kabul Amid Strained Relations VOA News March 07, 2011 General Petraeu, Commander of ISAF Afghanistan, chats with US Defense Secretary Gates upon Gates' arrival in Kabul, March 7, 2011 Photo: Reuters General Petraeu, Commander of ISAF Afghanistan, chats with US Defense Secretary Gates upon Gates' arrival in Kabul, March 7, 2011 U.S. Defense Secretary Robert Gates arrived in the Afghan capital, Kabul, Monday. Officials say his trip will focus on preparations for the transfer of security responsibility to Afghan forces, which is due to start in July. Gates will visit several areas where authorities say Afghan troops are playing a larger role in military operations and new local police units are beginning to have an impact. The defense secretary will also meet with Afghan President Hamid Karzai and senior U.S. And NATO commanders. Gates' trip to Afghanistan comes at at time of strained relations between the South Asian nation and the U.S., following the mistaken killing of nine Afghan boys during a NATO airstrike in northeastern Kunar province last Tuesday. President Karzai told General David Petraeus, commander of U.S.-led NATO forces in Afghanistan, Sunday that his apology for the deaths of the boys was "not enough." The Afghan leader said civilian casualties resulting from NATO military operations are "no longer acceptable." The killing of the boys, who were mistaken for insurgents while collecting firewood, sent hundreds into the streets of Kabul, Sunday. Protesters shouted "Death to America." .