A powerful bomb explosion outside a girls ' school has left nearly a dozen children wounded in Pakistan ' s troubled northwestern tribal region, security sources say.The sources said the bomb went off at in the northwestern town of Bannu located in Khyber Pakhtunkhwa Province on Thursday. At least 11 children were shifted to a nearby hospital for medical treatment. Law enforcement agents cordoned off the area after the blast and launched an investigation. No individual or group has claimed responsibility for the attack so far. Tehrik-e Taliban Pakistan (TTP) militants are the main suspects in the incident. The TTP has banned female education in northwestern Pakistan in a move that has affected thousands of girls there and caused the number of enrolments to drop dramatically. The group warns parents against sending their daughters to schools, describing education as 'unnecessary' and 'harmful' for girls. Over the past several years, TTP militants have destroyed hundreds of schools, especially in Khyber Pakhtunkhwa Province. In December 2012, Pakistan and UNESCO unveiled the Malala Plan, which aims to get all the girls in the world into school by the end of 2015. Militants have carried out numerous attacks against security forces as well as civilian institutions, and managed to spread their influence in various regions of the country, despite frequent offensives by the Pakistani Army. Thousands of people have lost their lives in bombings and other militant attacks since 2001 when Pakistan entered an alliance with the US on the so-called war against terrorism, according to local media. Since late 2009, there has been a surge in militant attacks in Pakistan and thousands more have been displaced by the wave of violence and militancy sweeping across the country.