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. Top US Military Official in Afghanistan 25 July 2010 Gen. Ashfaq Parvez Kayani, Pakistani chief of Army Staff points out a feature to Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff during an aerial tour of Northern Pakistan, 24 Jul 2010 Photo: DOD/Chad J. McNeeley Gen. Ashfaq Parvez Kayani, Pakistani chief of Army Staff points out a feature to Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff during an aerial tour of Northern Pakistan, 24 Jul 2010 The top U.S. military official has arrived in Afghanistan, where U.S.-led forces have been fighting Taleban and al-Qaida militants since late 2001. Joint Chiefs of Staff Chairman Admiral Mike Mullen began his visit Sunday in the eastern city of Jalalabad where he told the troops their tour of duty this year comes at a critical time.  He said if the coalition force does not defeat the Islamic extremists, the militants will emerge stronger in the future.  Mullen said Saturday in neighboring Pakistan that despite plans to begin withdrawing U.S. troops from Afghanistan next July, the U.S. commitment to the region "will endure." He said the Afghan government and its coalition supporters are far from being strong enough yet to successfully negotiate with militant groups. Mullen said the final several thousand U.S. surge troops will be in Afghanistan soon. He said by the end of the year, more should be known on whether the surge strategy announced by President Barack Obama in December is creating a stronger position. .