One person was killed in Sri Lanka on Monday in the worst sectarian violence since the Easter Sunday bombings that killed more than 250 people. Police fired tear gas at anti-Muslim mobs that were attacking mosques and Muslim-owned shops in a backlash against the community after the deadly bombings, and the authorities imposed a nationwide curfew. Muslim residents in parts of the country's North Western Province accused the police and army of standing by while mobs attacked. "There are hundreds of rioters, police and the army are just watching. They have burnt our mosques and smashed many shops owned by Muslims," a resident told Reuters by telephone, asking not to be identified for fear of reprisals. "When we try to come out of our house, police tell us to stay inside." One man died after being admitted to hospital with stab wounds, an officer at Marawila hospital said. The man, 42, was identified as Mohammed Ameer Mohammed Sally by a resident who helped transport him to hospital. In response to the violence, the police imposed a nationwide curfew between 9pm and 4am local time, spokesman Ruwan Gunasekera said. Prime Minister Ranil Wickremesinghe said that they will take "strong action" and that acts of sabotage were hampering an investigation by security forces. "If the racism rises up ... and peace is disturbed the country will be destabilised," he said. "The intention of these groups who are causing violence is to cause disruption in public life." Mr Wickremesinghe said he had given powers to the security forces to take strong action against those disturbing the peace. On Monday, the Sri Lanka government blocked social media across the country. It is the third time it has done so since the Easter Sunday attacks, when Isis-linked militants bombed three hotels and three churches while Catholics were celebrating one of the holiest days of the year. On Monday night, the pale-pink Abar mosque was attacked in the town of Kiniyama. The windows were smashed and broken glass and copies of the Quran were strewn across the floor. A 34-year-old man who was at the mosque said that on Sunday around 150-200 people marched on the mosque with rods and swords, but attendees to the mosque persuaded them to leave with the help of police. However, a larger mob of around 1,300 people returned on Monday. Muslims huddled in the mosque for safety and requested that police fire their guns in the air to disperse the mob, but police refused, saying that the mob wanted to inspect the mosque for weapons. The witness said the crowd then surged into the mosque and ransacked it. "They destroyed and burnt Qurans, broke every glass window and door and urinated on the water storage, which Muslims used to take ablution," he said. Police spokesman Mr Gunasekera did not respond to a request for comment on the incident, but in an emailed statement to Reuters he said there had been some damage to property in the Hettipola area of Kurunegala district. It said that no injuries had been reported and that police had fired in the air in the Hettipola area.