Beijing, June 22 : Nine people were detained in Thursday over a massive explosion at a barbecue restaurant in China's Yinchuan city which killed at least 31 people. Authorities said that the detained persons included the owner of the Fuyang Barbecue Restaurant, as well as staffers and shareholders of the eatery, reports Xinhua news agency. Assets of the nine people have also been frozen. Verification of the identities of the victims is underway and local authorities are also conducting an investigation into the cause of the accident. The explosion occurred at around 8.40 p.m. on Wednesday due to an alleged gas leak at the restaurant which is part of a cluster of eateries and entertainment venues in Yinchuan, the capital of the Ningxia autonomous region. Seven injured persons are currently being treated at a hospital. The detentions came shortly after President Xi Jinping demanded to hold the relevant people accountable in accordance with the law. He also called for maximum efforts in treating the wounded and boosting safety measures. "We must do our best to rescue the injured and reassure the families of the casualties, identify the cause of the accident as soon as possible, and seriously pursue responsibility according to the law," the BBC quoted Xi as saying. Fire and rescue services dispatched more than 100 personnel and 20 vehicles to the scene, the Ministry of Emergency Management said. The rescue operation lasted until 4 a.m. on Thursday. /IANS