Afghan security forces had blocked the attacker from approaching a crowd of about 150 people who had gathered for a ribbon-cutting ceremony to open an emergency ward at the main government hospital in the city of Khost, said Gov. Arsalah Jamal. He said US troops who took the man away shot him in the leg when he tried to escape. As the crowd took cover, the attacker blew himself up, Jamal said. He said two American soldiers and an Afghan hospital staffer were wounded. Sgt. 1st Class Dean Welch, a NATO spokesman, said a number of NATO troops were wounded in the blast, but the extent of their injuries was not immediately known. He did not give their nationalities. Most of the NATO forces in eastern Afghanistan are American. Jamal said the attacker looked about 16 years old. Provincial police chief Gen. Mohammad Ayub said the bomber was wearing a white coat of the same type used by doctors in the hospital and had possibly stayed the night inside the facility before launching his attack. Last year, Taliban-led militants launched about 140 suicide attacks, mostly targeting foreign and Afghan forces and officials of President Hamid Karzai's government - part of a wave of violence that made 2006 the bloodiest year here since the ouster of the hardline regime in 2001.