The death toll in four days of clashes between rival Muslim factions in northern Yemen has risen to 55, as the government tries to broker a ceasefire in a region that lies largely outside its control.

Shia Muslim Houthi rebels launched an attack on the town of Dammaj, held by their Sunni Muslim Salafi rivals, on Wednesday.

The army said earlier that a ceasefire had come into effect on Friday afternoon, but a Salafi spokesman then said clashes had continued on Saturday, and that a total of 55 people from his group had been killed by rockets and tank fire.

Yehia Abuesbaa, the head of a presidential committee tasked with ending the fighting, said a ceasefire was now expected to come into effect on Sunday.

He said the Houthis had sought the release of six of their followers who had been kidnapped by pro-Salafi fighters from a third group, al-Ahmar, in the neighbouring province of Omran. They were freed following the intervention of President Abd-Rabbu Mansour Hadi, Abuesbaa said.

The al-Ahmar group includes both Sunni and Shia Muslims, and its members are key figures in the Sunni Islah party.

Protests at president's home

Dozens of protesters demonstrated outside the president's home on Saturday, calling for more action to be taken by the government to stop the violence.

There was no immediate independent account of Saturday's clashes or report of Houthi casualties in Dammaj, which lies in Saada, a mountainous province that has long been outside central government control.

Ali al-Imad, a Houthi spokesman, accused the Salafis of being "foreign extremists" who consider his Shia group "heretics".

"They're clearly trying to drag the country into a Sunni-Shia war," he said.

But the Salafis say the foreigners within them are students who came to study Islamic theology in a seminary built in the 1980s.

They say Dammaj, which is near the Houthi-controlled city of Saada near the Saudi border, has been under rebel siege for weeks and say their rockets have hit, among other targets, student dormitories at a religious school.

Apart from the Salafi-Houthi conflict, Yemen is struggling with southern secessionists and al-Qaeda fighters in the Arabian Peninsula.