Gunmen attacked the Pakistan Stock Exchange in Karachi today, lobbing a grenade onto the trading floor and killing three security officers, authorities said. Reports indicate that six people were killed, including four attackers and a policeman, as brokers sheltered in offices. The Baluchistan Liberation Army claimed responsibility for the carnage, demanding independence for the country's restive province with abundant gas reserves. Authorities said the gunmen were carrying food, suggesting they planned a prolonged siege. Among the group's grievances is China's Belt and Road Initiative, which is spending billions to build a road that runs through Baluchistan.