Israeli soldiers are on high alert after a bus blast kills at least four on the Egyptian side of the border.<br/> <br />Officials said the attack killed three Koreans and the Egyptian driver.<br/> <br />The bus was heading from a popular tourist destination in the south Sinai to the Taba crossing.<br/> <br />Nobody claimed responsibility for the blast, but al Qaeda-inspired Islamist militants have carried out several attacks there in recent months.<br/> <br />The incident remains under investigation.
