The blast caused minor damage to the wall but no casualties, he said. The 200-bed Christian Missionary Hospital has been operating in Tank, some 400 kilometres south of here, since 1945. Local police officer Mohammad Khan told AFP by telephone that such devices were made in the tribal area. An investigation was underway to track down the perpetrators, he said. Pakistan's Christian community has suffered a string of attacks by suspected Islamic militants wreaking revenge for the United States-led ouster of neighbouring Afghanistan's Taliban regime in late 2001. Deadly strikes on Christian institutions, including four churches, a school for foreign missionaries' children and a welfare centre, have claimed the lives of 41 people, including two Americans and Muslims guarding the centres.