At least 71 people, including five children and 15 foreigners, have been killed by Shiite attacks on a Sunni Islamic school in north Yemen since mid-October, a spokesman for the school said on Wednesday.
Al-Sorur Wadii told AFP that Zaidi Shiites, also known as Huthis, have surrounded the town of Dammaj for more than two months and launched several attacks on its Dar al Hadith Sunni fundamentalist institute.
He said that the rebels have also prevented food, water, and other basic supplies from entering the town.
"In total, 71 people, including five children and one woman, have been killed, and 165 others have been wounded," said Wadii, adding that "15 foreigners, including four to six Russians, three Algerians, a Frenchman, a Malaysian, a Somali and Americans" were among the dead.
He said Dammaj, south of Shiite rebel stronghold Saada, "has been under siege for 67 days and is completely surrounded by Huthis," who accuse Sunni leaders in the area of proselytising in Shiite-majority areas.
Dar al-Hadith is an Islamic institution that trains Sunni preachers and believes in the strictest and most draconian interpretations of Islam.
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There have been fierce clashes between the two sides despite mediation by local tribesman trying to ensure the supply of food and medicine to Dammaj.
However, the conflict appears to be escalating.
On Wednesday, medium and large-calibre weapons were used in Sunni-Shiite clashes in the town of Kitaf, some 70 kilometres (40 miles) east of Saada, local tribal leader Sheikh Abdullah al-Hudeish told AFP.
He said sectarian tensions in the area were running high since Shiite rebels "blocked the road to prevent humanitarian assistance from reaching Dammaj," which has a population of some 10,000.
Other tribal sources said 26 Salafists, Sunni fundamentalists, were killed in an attack on Dammaj by rebels on November 27.
Shiite rebel forces lost five men earlier this month, the same sources said.
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.