Bangkok, May 22 (IANS) At least 24 persons were injured in an explosion in Phramongkutklao Hospital in Bangkok on Monday, police said.The blast took place in a reception room, Xinhua news agency quoted Saroch Kheawkhajee, chairman of the Army Medical Department, as saying.A gas leak or an air compressor may have caused the explosion, he said.An investigation has been initiated to determine the exact cause of the incident.