A youth was critically injured in a knife attack at Adarsanagar in Birgunj today morning. 25-year-old Bishal Shah from Chhapkaiya, Birgunj-1 was injured when he was attacked by a group of youths. Shah was out for morning walk when he was attacked with sharp weapons, including a knife near a swimming pool. District Police Office Parsa said that a group of youths including Rishikesh Patel and Dinesh Patel from Sirsiya had assaulted Shah over old animosity. Bishal has received serious cuts on his waist, right hand and right stomach. Sah was referred to another hospital after he could not be treated at Birgunj-based Narayani Sub-regional Hospital, said DSP Hobendra Bogati. Police have arrested locals Sagar Patel, Arun Patel, Sagar Shah and Dilip Kumar Shah for their alleged involvement in the incident. The arrested have been kept in the custody of Ward Police Office Birta.