New Delhi, Aug 27 : Special Cell of Delhi Police will probe the pro-Khalistan graffiti incident which appeared at several metro station in nation capital on Sunday. The Delhi Police has lodged FIR under sections 153, 153A, 505 IPC and section 3 of Defacement Act. 'Seeing the gravity of the matter, Special Cell has been asked to probe the incident. Sikh for Justice (SFJ) activists can be behind the incident. Cell is already probing cases related to SFJ,' a police official said. Pro-Khalistan graffiti appeared at various metro stations in the national capital on Sunday. The graffiti appeared at more than seven stations and near a government school as well. The police have removed all the graffiti ahead of the G20 Summit in the national capital. The derogatory graffiti slogans challenging the sovereignty of India appeared at following metro stations: ShivaJi Park, MadiPur, Paschim Vihar, Udyog Nagar, and Maharaja Surajmal Stadium; Punjabi Bagh and Nangloi Metro Stations. Graffiti had also appeared at government Sarvodya Bal Vidyalya Nangloi. /IANS