SANAA, Yemen - Twenty gunmen were killed Thursday in clashes between Zaidi Shiite rebels and Sunni Salafist gunmen in northern Yemen, a security official said. Clashes erupted in the morning in the northwestern Hajjah province between rebel gunmen, known as Huthis, and Sunni extremists, the local official told AFP. The official said the gunfight took place in the city of Mustaba, close to the Red Sea port city of Midi, at the border with Saudi Arabia. Other clashes erupted between the Sunni Waela tribe and Shiite rebels in the province of Saada, the stronghold of the rebels. Fighting between the Sunni fundamentalists and the Huthi rebels had raged over the past months in the northern town of Dammaj, south of Saada, where a Salafist Islamic teaching school was besieged by Huthi rebels.At least 71 people were killed in clashes that erupted in mid-October, a spokesman for the Dar al-Hadith school claimed in late December. The school trains Sunni preachers and believes in the strictest and most draconian interpretations of Islam.In 2004, Zaidi Shiites, who regularly complain of inequality and marginalisation by the central government, rebelled against President Ali Abdullah Saleh’s regime.Thousands of Yemenis were killed before a ceasefire was declared in February 2010.