At least four foreign nationals have been killed and five security personnel injured in a bomb blast in northwest part of Pakistan on Wednesday while at least 31 people have been killed in US drone attack in its tribal areas.<br/><br/>The explosion took place near Koto Girls School in Balambut area of Lower Dir. Three of those killed in the blast are reported to be journalist.<br/><br/>The nationalities of those killed in the explosion is not clear.<br/><br/>Several students are reportedly trapped inside the damaged school building even as security forces have cordoned off the area. <br/><br/>In one of the biggest US drone attack so far in its tribal areas, at least 31 people have been killed. The dead included 17 militants.<br/><br/>Secutiry officials said the strike, which involved 18 missiles were fired from eight unmanned planes in Dattakhel village in northwestern tribal region near the Afghan border on Tuesday. Earlier reports had put the death toll at 17. <br/><br/>Geo TV said that several of the injured persons are still fighting for their lives and the death toll is likely to go up. <br/><br/>The villagers came under attack from the drones while approaching the spot to help retrieve the bodies and the injured from the rubble of the collapsed houses.<br/><br/>Tribesmen in Miramshah, the main town of North Waziristan said the town echoed with heavy explosions when the missiles were fired.