Two days of clashes between Shiite rebels and Sunni tribesmen fighting alongside hardline Salafists in northern Yemen have left at least 23 people dead, sources said on Sunday.
Fighting has centred for months on a Salafist mosque and Koranic school in Dammaj, which has been besieged by the Shiite rebels known as Huthis.
But the conflict has spread in the northern provinces, embroiling Sunni tribes wary of the power of the Huthis, who have repeatedly been accused of receiving support from Iran.
On Sunday, at least 10 people were killed in Jawf province in clashes between rebels and armed men from the Daham tribe, a tribal chief told AFP.
Seven people were killed at Harf Sufyan, in the northern province of Amran, another tribal chief said on Sunday, while two others died in shelling of Dammaj, in Saada province, Salafist websites reported.
Four people died in fighting that took place in Jawf on Saturday, another tribal chief said.
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Huthi rebels this week took over positions evacuated by Salafist gunmen in the area of Kitaf, north of Saada city, witnesses said, adding the rebels demolished the Salafist Dar al-Hadith religious school and 20 houses.
The rebels have also warned border guards to evacuate the Bart al-Anan crossing point with Saudi Arabia, in Jawf, according to the head of the force, Colonel Qassem Thawaba.
The officer told AFP he refused to leave, insisting on waiting for orders from his command.
Fighting between Huthi rebels and tribesmen, alongside fighters from the Islah Islamist party, is ongoing as well in Arhab, about 30 kilometres (18 miles) north of Sanaa.
Huthis have been battling the central government for nearly a decade in remote Saada province, but the latest fighting between the rebels and the Salafists has given an added sectarian dimension to the clashes.
Analysts have said the Huthis are trying to control more territory in the north in anticipation of a forthcoming conclusion of a national dialogue that could turn Yemen into a federation of regions.
President Abdrabuh Mansur Hadi dispatched on Saturday mediators to the troubled areas.