Karachi- Muttahida Quami Movement (MQM) observed a mourning day today, against killing of its four activists. Karachi, Hyderabad, Sukkur, Nawabhshah, Mirpurkhas and other towns remained closed. All markets remained closed in Karachi. Public transporters, private schools, petrol pumps and gas stations also remained shut. Educational institutions were also off and many scheduled exams were postponed. Police and law enforcement agencies remained on high-alert and patrolled the city.