* Fighting in northern Saada province for second day
* Houthi rebels say Salafis bringing in foreign fighters
* In south Yemen suspected Qaeda militants kill 3 soldiers
The death toll from a Shi'ite Muslim Houthi attack on a mountain town in north Yemen held by their Salafi Sunni Muslim rivals has risen to 24, a Salafi spokesman said on Thursday as the two sides fought for a second day.
Fighting erupted despite government mediation efforts to shore up a ceasefire in place since late last year in a province long beyond the control of the authorities in Sanaa, capital of the turbulent Arabian Peninsula state.
Salafi spokesman Abu Ismail al-Hajouri said more than 100 people were also wounded in the town of Damaj, which he said the Houthi rebels, who dominate the northern province of Saada, had besieged for weeks.
He said most of the casualties had been inflicted in the past two days when rockets and tank shells hit a mosque and dormitories for students at a nearby religious school. He said Salafis were fighting back with light automatic weapons.
There was no independent account of the clashes and no immediate report on any Houthi casualties.
The Red Cross called for an immediate halt to the fighting to allow emergency assistance for the injured and to assess the humanitarian situation.
"We are in contact with all sides to ensure an end to the fighting and our team is in Saadeh and ready to enter the area, but cannot in light of the fighting," a spokeswoman for the International Committee of the Red Cross in Sanaa said.
A Houthi statement late on Wednesday accused the Salafis of igniting strife by bringing thousands of foreign fighters to Damaj, which lies near Saada, a Houthi-controlled city near the Saudi border 130 km (80 miles) north of the Yemeni capital.
The Salafis say the foreigners are students there to study Islamic theology in a seminary built in the 1980s.
"Many of the wounded are in serious condition and we can't move them to hospitals because the Houthis are surrounding the area," Hajouri, the Salafi spokesman, said by telephone.
The Houthis blockaded Damaj for weeks last year, accusing the Salafis of stockpiling weapons, a charge they deny.
A member of a mediation committee set up by President Abd-Rabbu Mansour Hadi blamed the Houthis for the latest flare-up.
"The Houthis caught the Salafis by surprise when they bombed Damaj with heavy weapons," he said, declining to be named. "We are trying to stop the confrontations."
Officials said fighting continued around Damaj on Thursday, and the government urged all parties to cease violence.
Saada province is the base for a long-running Houthi rebellion against the Yemeni government. Saudi Arabia's military intervened in 2009 before a ceasefire took hold the year after. The province has since fallen openly into Houthi hands with a Houthi-imposed governor.
Some Sunnis fear the Houthis, who are named after their late leader, Hussein Badreddin al-Houthi, want to revive the 1,000-year Zaydi Imamate, whose rulers claimed descent from the Prophet Mohammad. The imamate ended in a 1962 military coup.
Apart from the Salafi-Houthi conflict, Yemen is struggling with southern secessionists and militants of al Qaeda in the Arabian Peninsula, which has plotted attacks on U.S. airliners and targets in Saudi Arabia, the world's top oil exporter.
On Thursday, suspected al Qaeda militants attacked an army checkpoint in the southern province of Abyan, killing three soldiers, a local official and residents said. They said the assailants had withdrawn taking their casualties with them.