Sectarian fighting has erupted between Shia Houthi rebels and Sunni fighters in northern Yemen, shortly after a UN-brokered ceasefire was announced, both sides said on Tuesday.
The agreement to end the fighting in the town of Damaj allowed Red Cross aid workers to evacuate the critically wounded.
"The ceasefire collapsed after few hours," Houthi spokesman Ali al-Bakheeti told the AFP news agency.
He accused foreign Salafist fighters, allegedly based in Damaj, of violating the truce announced on Monday by the UN special envoy to Yemen, Jamal Benomar.
A spokesman for the Salafists in Damaj accused the Shia rebels of violating the ceasefire.
"The truce lasted only two hours, due to the Houthis' intransigence," Sourur al-Wadii said by telephone from Damaj.
The clashes in Damaj broke out on Wednesday when Shia Houthi fighters, who control much of the border province of Saada, accused their Sunni Salafi rivals of recruiting thousands of foreign fighters to attack them.
The Houthis have been battling Yemen's central government for nearly a decade, but the outbreak of fighting with Sunnis has amplified the sectarian dimension of the conflict in the remote northern province.
Besieged by the Houthis
A Red Cross convoy entered the village - where the Islamists are besieged by the Houthis - on Monday and the aid group said its teams had evacuated 23 critically wounded people.
"There are still more wounded people in need of treatment, and we hope to be able to come back for them," the International Committee of the Red Cross's director in Yemen, Cedric Schweizer, said in a statement.
Tribal sources said at least 11 people were killed in fighting last week, but Sunni fighters put the death toll at around 50.
The fighting with mortar and rocket fire was concentrated around the Mazraa mosque and a Quranic school held by the Islamists in Damaj and surrounded by rebels.
Benomar said on Monday he hoped the ceasefire would last, warning the conflict "threatens the security of Yemen”.
The Houthis, who are members of the Zaidi Shia community, rose up in 2004 against former president Ali Abdullah Saleh's government, accusing it of marginalising them politically and economically.
Saleh, a western ally, was succeeded by the current president, Abd-Rabbu Mansour Hadi, following a violent uprising against his regime.