Suicide attackers stormed a mosque in Rawalpindi, close to the army headquarters, during Friday prayers and killed at least 40 people, including some top military officials.
No previous terror attack in Pakistan has led to so many casualties among armymen, police officials said.
But the army so far has refused to share details of the persons killed. They have only confirmed the death of Major General Bilal Umar, director-general of the Armoured Corps.
The son of the commanding officer of the Pakistan forces fighting militants in Waziristan was also killed in the blast, sources said, though details are still awaited.
There were at least four attackers who clandestinely entered the mosque and set off bombs on the first floor, apart from firing indiscriminately.
“They are taking revenge for the Pakistan army’s successful operations in the Swat and Waziristan regions,” said interior minister Rehman Malik.