At least four Sunni Muslims were killed and over 15 others injured as a bomb went off in a shrine in Pakistan's southern district of Shikarpur on Monday night, local media reported. Geo TV said the sectarian blast targeting the Sunni Muslims occurred when over 50 people were gathering in a congregation hall of the shrine for religious ritual. Some unknown militants left an explosive laden bag inside the shrine and later exploded it by a remote control, said the report. The injured people were shifted to Civil Hospital Shikarpur where several of them were in critical conditions. Walls and roof of the shrine were partially destroyed in the blast in Shikarpur, a main district in the country's southern Sindh province. The blast was followed by a protest by Sunni Muslims in the district. Sahabzada Fazal Karim, the leader of the country's prominent Sunni group, "Sunni Itehad Council", condemned the blast and asked his followers to remain calm. He also demanded government to arrest those responsible for the attack. No group so far claimed responsibility for the attack. Police cordoned off the area and a probe into the incident has been started.