( 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 can not indulge in any political agreement with an armed movement . How can we involve them into politics when they do n'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 .
Dozens killed when militants raid a Sunni town . At least 61 people are injured when their homes are shelled with grenades . Doctors could not reach the injured because the town is under siege . Saleh returns to Yemen on Saturday night .