Shiite rebels killed 20 people and wounded 70 others in an attack on a Sunni Islamist school in northern Yemen, a tribal source said on Sunday. The attack targeted the Dar al-Hadith school, a Muslim fundamentalist centre set up in the 1980s to train Sunni preachers in Dammaj, a suburb of the Shiite stronghold city of Saada, said the same source. Dar al-Hadith, which is attended by students from Yemen and many other countries, is seen as a Sunni threat by Shiite Huthis who dominate the northern region. A teacher at Dar al-Hadith told AFP on condition of anonymity that before launching the attack the Huthis had blocked off the Dammaj suburb for two weeks, preventing the delivery of food to about 10,000 people. According to the teacher, the Huthis want to shut down such religious schools because they fear that Sunnis are trying to convert the Shiites in the region.