Bangkok: At least four persons were killed and 15 injured as multiple explosions struck Thai tourist towns on Friday. Police have detained two suspects for being involved in the blasts. A string of explosions occurred as Thailand celebrated the Queen's birthday, Bangkok Post reported. Friday's explosions came just hours after one person was killed and nearly 20 injured, including foreign tourists, in two explosions in Hua Hin town on Thursday night. At least eight explosions hit three cities in 12 hours, the police said. "The blasts in Prachuap Khiri Khan and other southern provinces were not terrorist acts, but of sabotage," Pol Maj Gen Piyaphan Pingmuang, deputy spokesman for the Royal Thai Police, said. He said that Thailand had no conflict over race and religions among ethnic minorities or was under threat linked to Islamic State terrorism. The explosions stemmed from internal conflicts and were aimed at creating chaos, he said. Thai Prime Minister Prayut Chan-o-cha said some Thais "without hearts" were making trouble, adding that the government would do its utmost to secure the kingdom. National police chief Chakthip Chaijinda instructed all police agencies to tighten security at government offices and symbolic places, particularly bus terminals, railway stations, airports, tourist attractions and areas frequented by tourists. The explosions began on Thursday night in the resort of Hua Hin. Two bombs placed near a local bar called Johnny's 56 went off as tourists were leaving to go back to their hotels, CNN quoted Police Lieutenant Colonel Samoer Yoosumran as saying.