At least four people were killed and five others injured Saturday when a suicide bomber blew herself up at the gates of a hospital in north-west Pakistan, officials said.The blast took place in Khar, the main town in the province of Bajaur.Mohammed Riaz, the head of Khar district hospital where the attack occurred, told DPA he had received the bodies of the four dead.\"Two hospital staffers, one paramilitary soldier and one civilian are among the dead,\" Riaz said. \"One of the five who were injured is also in critical condition.\"\"We have recovered the limbs of a female suicide bomber from the scene,\" Asad Sarwar, a district official, said.No one has claimed responsibility for the blast.