At least four persons have been killed and 12 injured after an LPG cylinder exploded at a village in Uttar Pradesh's Agra district, police said on Tuesday.The incident took place in Daadhki village in Iradatnagar around midnight apparently due to leakage in the gas cylinder.The deceased have been identified as Kamal Singh, 45, Girraj Singh, 61, Mahaveer, 40, and Om Prakash, 27.Of the injured, the condition of three is critical, a police officer told IANS, adding the injured have been admitted to S.N. Medical College in Agra.The explosion took place at the house of Himmat Singh. His daughter Meera was cooking when she noticed the gas leakage, and the pipe to the cylinder catching fire.She raised an alarm, hearing which many people came to the rescue but before they could do anything, the cylinder exploded.Due to the impact of the explosion, the two-storey house of Singh was flattened.