Kolkata: A section of junior doctors and interns at the state-run SSKM Hospital here launched an "indefinite strike" on Thursday following an alleged assault on one of their colleagues by a family members of an admitted patient. Demanding adequate security, the agitators claimed Abhishek Singh, an intern was beaten up by several relatives of a six-year-old boy from North 24 Parganas who was brought into the emergency ward on Wednesday night. The patient's family claimed the doctors had delayed treatment of the child who was injured in an accident. A complaint was lodged at the Bhowanipore police station. The junior doctors also laid siege at senior physician's cabin through Wednesday night demanding proper security. Later, a delegation of the protesting junior doctors submitted a deputation to the SSKM Director over steeping up security and averred they would continue the strike till their demands are met, said an agitating doctor.