Chief of Army Staff General Qamar Bajwa directed army men to assist rescue personnel after a powerful blast ripped through a crowded Sufi shrine in Sindh.
Police said a suicide bomber killed at least 72 people and wounded dozens more within the premises of Lal Shahbaz Qalandar shrine in the latest in a wave of bombings this week.
"Your security forces shall not allow hostile powers to succeed. We stand for our nation," Inter-Services Public Relations quoted the army chief as saying.
Recent Ts acts are being exec on directions from hostile powers and from sanctuaries in Afghanistan. We shall defend and respond.— Maj Gen Asif Ghafoor (@OfficialDGISPR) February 16, 2017
#COAS, "Each drop of nation's blood shall be revenged, and revenged immediately. No more restraint for anyone."— Maj Gen Asif Ghafoor (@OfficialDGISPR) February 16, 2017
Local media quoted a medical superintendent identified as Moinuuddin as saying at least 50 bodies and 75 seriously wounded were brought to a local hospital.
Senior police officer Shabbir Sethar told Reuters from a local hospital that the death toll was likely to rise.
"At least 72 are dead and over 150 have been injured," Sethar said by telephone.
Islamic State, which said it had carried out last year’s Shah Noorani shrine attack in Balochistan claimed responsibility for the attack, reported Amaq News agency.
Several other attacks this week, including a bomb that killed 13 people in the eastern city of Lahore, were claimed by the Taliban's Jamaat-ur-Ahrar faction.
PM condemns attack
Prime Minister Nawaz Sharif immediately condemned the attack on Lal Shahbaz Qalandar in the town of Sehwan in Sindh.
"The past few days have been hard, and my heart is with the victims," he said.
"But we can't let these events divide us, or scare us. We must stand united in this struggle for the Pakistani identity, and universal humanity."