(CNN) -- At least 24 people were killed early Sunday when militants raided a Sunni town in northern Yemen, medics and witnesses said.
The Houthi Shia militants raided a Sunni town in Sa'ada in the predawn hours, medics said.
At least 61 Sunnis are also injured when their homes were shelled with grenades, the medics said.
They medics did not want to be named because they are not authorized to talk to the media.
Witnesses said the injured did not get medical attention because the town was under siege.
The Houthi attacks were concentrated on a Sunni religious center, according to witnesses.
All mediation efforts to end the conflict have failed.
Houthis, a pro-Shia movement in Yemen, has expanded during the 10-month struggle to oust the president.
Opposition officials have expressed concern over its growth.
"We cannot indulge in any political agreement with an armed movement. How can we involve them into politics when they don't believe in it," said Ali Mamari, an opposition member in Yemen.
Mamari said Yemenis will not accept movements that spread with force and kill people.
"There is no difference between Houthis and al Qaeda, both are armed and use force to spread their beliefs," he said.
Houthis rejected the power transfer signing that took place in Riyadh earlier this week and said it would not recognize it.
"The movement has more than 100,000 fighters ready to obey commands from their spiritual leader, Abdul Malik al-Houthi," said Ahmed Bahri, an expert in Houthi affairs.
"This movement is well organized and only has one head," Bahri said.
"They now control majority areas in the provinces in Sa'ada and Jawf, and have powerful presence in Amran, Mareb, Sana'a and Hajjah," added Bahri.
Sectarian violence is at peak in northern Yemen where Houthis control is spread across five provinces.
Saudi Arabia fought the Houthis in 2009 but failed to end their expansion.
The attacks come a day after Yemen's vice president called for presidential elections to be held in February, state media reported.
President Ali Abdullah Saleh stepped down after months of protests against his 33-year rule. He became the fourth leader to leave office as a result of the Arab Spring unrest that has roiled much of the Middle East and North Africa this year.
Saleh returned to Yemen on Saturday night, days after he signed an agreement in Saudi Arabia yielding his powers, according to the Yemen official news agency