The militants first drove to Qasim Bela area in Multan, the home town of Premier Yousuf Raza Gilani and Foreign Minister Shah Mahmood Qureshi in Punjab province, in a truck and attacked security personnel manning a check post with small arms and rockets.
They then drove up to the ISI office situated within the high-security cantonment area and lobbed grenades before blowing up their explosives-laden vehicle, police said. Twelve people, including four soldiers and four children, were killed in the attack, said officials of the state-run emergency services.
Forty seven injured people, including women and children, were taken to three nearby hospitals. Four of them were in a serious condition.
This was the second attack targeting ISI in less than a month. On November 13, suicide bombers struck its operational headquarters in northwestern city of Peshawar, leaving 12 people dead and 65 injured.
Today's attack follows the suicide bombing at a crowded market in Lahore last night that killed 49 people and injured 180 others. Another suicide bomber blew himself up outside a court complex in Peshawar yesterday, killing 10 people.