More than 100 people have been arrested in Pakistan after a Sri Lankan factory manager was beaten to death and set ablaze by a mob who accused him of blasphemy, officials said on Saturday. The vigilante attack has caused outrage, with Prime Minister Imran Khan calling it a "day of shame for Pakistan". The incident took place on Friday in Sialkot, a district in central Punjab province, about 200 kilometres south-east of the capital, Islamabad. "Rumour spread in the factory that the manager had torn down a religious poster and thrown it in the dustbin," Zulfiqar Ali, a police official in the area, told AFP. Police spokesman Khurram Shehzad said up to 120 people had been arrested, including one of the main accused, and that raids were continuing. Tahir Ashrafi, a religious scholar and special representative of the prime minister on religious harmony, confirmed the arrests and said that workers had complained of the manager being "very strict". "Police experts are investigating this case from various angles, including that some factory workers played a religious card to take revenge on the manager," Mr Ashrafi said. Several gruesome video clips shared on social media showed a mob beating the prone victim while chanting slogans against blasphemy. Other clips showed his body set ablaze, as well as the overturned wreckage of what was said to be his car. Many in the mob made no attempt to hide their identity and some took selfies in front of the burning corpse. Hasaan Khawar, a spokesman for Punjab government, told reporters on Saturday that 800 to 900 people, some of them armed with sticks, were seen dragging the body of the manager. He said a post-mortem examination of the body had been done and the body would be handed over to the Sri Lankan embassy in Islamabad. Malik Naseem Awan, a resident and lawyer in Sialkot, told AFP he was worried about the impact it would have on the country's image. "I can't tell you how embarrassed I am. It would have been different if someone had done this individually but the crowd present there was watching it silently, and no one tried to rescue him," he said. The incident was condemned by almost all of Pakistan's political and religious parties, as well as head of the army. Sri Lanka's president and prime minister expressed shock over the "brutal and fatal attack" and asked Pakistan to punish all those involved. A senior Pakistani official told AFP that Islamabad had been in touch with Sri Lankan diplomats over the incident "and have assured them that all those involved in the heinous crime will be brought to justice". Rights groups say accusations of blasphemy can often be wielded to settle personal vendettas, with minorities largely the target. Last Sunday, thousands of people torched a police station in north-western Khyber Pakhtunkhwa province after demanding officers hand over a man accused of burning a copy of the Quran. In April 2017, a mob lynched a university student who was accused of posting blasphemous content online. A Christian couple was lynched then burnt in a kiln in Punjab in 2014 after being falsely accused of desecrating a Quran.